curl/docs/KNOWN_BUGS

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                                  Known Bugs

These are problems and bugs known to exist at the time of this release. Feel
free to join in and help us correct one or more of these. Also be sure to
check the changelog of the current development status, as one or more of these
problems may have been fixed or changed somewhat since this was written.

 1. HTTP
 1.5 Expect-100 meets 417

 2. TLS
 2.3 Unable to use PKCS12 certificate with Secure Transport
 2.4 Secure Transport will not import PKCS#12 client certificates without a password
 2.5 Client cert handling with Issuer DN differs between backends
 2.7 Client cert (MTLS) issues with Schannel
 2.8 Schannel disable CURLOPT_SSL_VERIFYPEER and verify hostname
 2.11 Schannel TLS 1.2 handshake bug in old Windows versions
 2.12 FTPS with Schannel times out file list operation
 2.13 CURLOPT_CERTINFO results in CURLE_OUT_OF_MEMORY with Schannel

 3. Email protocols
 3.1 IMAP SEARCH ALL truncated response
 3.2 No disconnect command
 3.3 POP3 expects "CRLF.CRLF" eob for some single-line responses
 3.4 AUTH PLAIN for SMTP is not working on all servers

 4. Command line

 5. Build and portability issues
 5.1 OS400 port requires deprecated IBM library
 5.2 curl-config --libs contains private details
 5.5 cannot handle Unicode arguments in non-Unicode builds on Windows
 5.9 Utilize Requires.private directives in libcurl.pc
 5.11 configure --with-gssapi with Heimdal is ignored on macOS
 5.12 flaky CI builds
 5.13 long paths are not fully supported on Windows
 5.14 Windows Unicode builds use homedir in current locale

 6. Authentication
 6.1 NTLM authentication and unicode
 6.2 MIT Kerberos for Windows build
 6.3 NTLM in system context uses wrong name
 6.4 Negotiate and Kerberos V5 need a fake user name
 6.5 NTLM does not support password with § character
 6.6 libcurl can fail to try alternatives with --proxy-any
 6.7 Do not clear digest for single realm
 6.9 SHA-256 digest not supported in Windows SSPI builds
 6.10 curl never completes Negotiate over HTTP
 6.11 Negotiate on Windows fails
 6.12 cannot use Secure Transport with Crypto Token Kit
 6.13 Negotiate against Hadoop HDFS

 7. FTP
 7.3 FTP with NOBODY and FAILONERROR
 7.4 FTP with ACCT
 7.11 FTPS upload data loss with TLS 1.3
 7.12 FTPS directory listing hangs on Windows with Schannel

 9. SFTP and SCP
 9.1 SFTP does not do CURLOPT_POSTQUOTE correct
 9.2 wolfssh: publickey auth does not work
 9.3 Remote recursive folder creation with SFTP
 9.4 libssh blocking and infinite loop problem

 10. SOCKS
 10.3 FTPS over SOCKS

 11. Internals
 11.2 error buffer not set if connection to multiple addresses fails
 11.4 HTTP test server 'connection-monitor' problems
 11.5 Connection information when using TCP Fast Open
 11.7 signal-based resolver timeouts
 11.16 libcurl uses renames instead of locking for atomic operations

 12. LDAP
 12.1 OpenLDAP hangs after returning results
 12.2 LDAP on Windows does authentication wrong?
 12.3 LDAP on Windows does not work
 12.4 LDAPS with NSS is slow

 13. TCP/IP
 13.2 Trying local ports fails on Windows

 15. CMake
 15.2 support build with GnuTLS
 15.3 unusable tool_hugehelp.c with MinGW
 15.4 build docs/curl.1
 15.6 uses -lpthread instead of Threads::Threads
 15.7 generated .pc file contains strange entries
 15.8 libcurl.pc uses absolute library paths
 15.11 ExternalProject_Add does not set CURL_CA_PATH
 15.13 CMake build with MIT Kerberos does not work

 16. Applications

 17. HTTP/2
 17.2 HTTP/2 frames while in the connection pool kill reuse
 17.3 ENHANCE_YOUR_CALM causes infinite retries

 18. HTTP/3
 18.1 connection migration does not work

==============================================================================

1. HTTP

1.5 Expect-100 meets 417

 If an upload using Expect: 100-continue receives an HTTP 417 response, it
 ought to be automatically resent without the Expect:. A workaround is for
 the client application to redo the transfer after disabling Expect:.
 https://curl.se/mail/archive-2008-02/0043.html

2. TLS

2.3 Unable to use PKCS12 certificate with Secure Transport

 See https://github.com/curl/curl/issues/5403

2.4 Secure Transport will not import PKCS#12 client certificates without a password

 libcurl calls SecPKCS12Import with the PKCS#12 client certificate, but that
 function rejects certificates that do not have a password.
 https://github.com/curl/curl/issues/1308

2.5 Client cert handling with Issuer DN differs between backends

 When the specified client certificate does not match any of the
 server-specified DNs, the OpenSSL and GnuTLS backends behave differently.
 The github discussion may contain a solution.

 See https://github.com/curl/curl/issues/1411

2.7 Client cert (MTLS) issues with Schannel

 See https://github.com/curl/curl/issues/3145

2.8 Schannel disable CURLOPT_SSL_VERIFYPEER and verify hostname

 This seems to be a limitation in the underlying Schannel API.

 https://github.com/curl/curl/issues/3284

2.11 Schannel TLS 1.2 handshake bug in old Windows versions

 In old versions of Windows such as 7 and 8.1 the Schannel TLS 1.2 handshake
 implementation likely has a bug that can rarely cause the key exchange to
 fail, resulting in error SEC_E_BUFFER_TOO_SMALL or SEC_E_MESSAGE_ALTERED.

 https://github.com/curl/curl/issues/5488

2.12 FTPS with Schannel times out file list operation

 "Instead of the command completing, it just sits there until the timeout
 expires." - the same command line seems to work with other TLS backends and
 other operating systems. See https://github.com/curl/curl/issues/5284.

2.13 CURLOPT_CERTINFO results in CURLE_OUT_OF_MEMORY with Schannel

 https://github.com/curl/curl/issues/8741

3. Email protocols

3.1 IMAP SEARCH ALL truncated response

 IMAP "SEARCH ALL" truncates output on large boxes. "A quick search of the
 code reveals that pingpong.c contains some truncation code, at line 408, when
 it deems the server response to be too large truncating it to 40 characters"
 https://curl.se/bug/view.cgi?id=1366

3.2 No disconnect command

 The disconnect commands (LOGOUT and QUIT) may not be sent by IMAP, POP3 and
 SMTP if a failure occurs during the authentication phase of a connection.

3.3 POP3 expects "CRLF.CRLF" eob for some single-line responses

 You have to tell libcurl not to expect a body, when dealing with one line
 response commands. Please see the POP3 examples and test cases which show
 this for the NOOP and DELE commands. https://curl.se/bug/?i=740

3.4 AUTH PLAIN for SMTP is not working on all servers

 Specifying "--login-options AUTH=PLAIN" on the command line does not seem to
 work correctly.

 See https://github.com/curl/curl/issues/4080

4. Command line

5. Build and portability issues

5.1 OS400 port requires deprecated IBM library

 curl for OS400 requires QADRT to build, which provides ASCII wrappers for
 libc/POSIX functions in the ILE, but IBM no longer supports or even offers
 this library to download.

 See https://github.com/curl/curl/issues/5176

5.2 curl-config --libs contains private details

 "curl-config --libs" will include details set in LDFLAGS when configure is
 run that might be needed only for building libcurl. Further, curl-config
 --cflags suffers from the same effects with CFLAGS/CPPFLAGS.

5.5 cannot handle Unicode arguments in non-Unicode builds on Windows

 If a URL or filename cannot be encoded using the user's current codepage then
 it can only be encoded properly in the Unicode character set. Windows uses
 UTF-16 encoding for Unicode and stores it in wide characters, however curl
 and libcurl are not equipped for that at the moment except when built with
 _UNICODE and UNICODE defined. And, except for Cygwin, Windows cannot use UTF-8
 as a locale.

  https://curl.se/bug/?i=345
  https://curl.se/bug/?i=731
  https://curl.se/bug/?i=3747

5.9 Utilize Requires.private directives in libcurl.pc

 https://github.com/curl/curl/issues/864

5.11 configure --with-gssapi with Heimdal is ignored on macOS

 ... unless you also pass --with-gssapi-libs

 https://github.com/curl/curl/issues/3841

5.12 flaky CI builds

 We run many CI builds for each commit and PR on github, and especially a
 number of the Windows builds are flaky. This means that we rarely get all CI
 builds go green and complete without errors. This is unfortunate as it makes
 us sometimes miss actual build problems and it is surprising to newcomers to
 the project who (rightfully) do not expect this.

 See https://github.com/curl/curl/issues/6972

5.13 long paths are not fully supported on Windows

 curl on Windows cannot access long paths (paths longer than 260 characters).
 However, as a workaround, the Windows path prefix \\?\ which disables all path
 interpretation may work to allow curl to access the path. For example:
 \\?\c:\longpath.

 See https://github.com/curl/curl/issues/8361

5.14 Windows Unicode builds use homedir in current locale

 The Windows Unicode builds of curl use the current locale, but expect Unicode
 UTF-8 encoded paths for internal use such as open, access and stat. The user's
 home directory is retrieved via curl_getenv in the current locale and not as
 UTF-8 encoded Unicode.

 See https://github.com/curl/curl/pull/7252 and
     https://github.com/curl/curl/pull/7281

6. Authentication

6.1 NTLM authentication and unicode

 NTLM authentication involving unicode user name or password only works
 properly if built with UNICODE defined together with the Schannel
 backend. The original problem was mentioned in:
 https://curl.se/mail/lib-2009-10/0024.html
 https://curl.se/bug/view.cgi?id=896

 The Schannel version verified to work as mentioned in
 https://curl.se/mail/lib-2012-07/0073.html

6.2 MIT Kerberos for Windows build

 libcurl fails to build with MIT Kerberos for Windows (KfW) due to KfW's
 library header files exporting symbols/macros that should be kept private to
 the KfW library. See ticket #5601 at https://krbdev.mit.edu/rt/

6.3 NTLM in system context uses wrong name

 NTLM authentication using SSPI (on Windows) when (lib)curl is running in
 "system context" will make it use wrong(?) user name - at least when compared
 to what winhttp does. See https://curl.se/bug/view.cgi?id=535

6.4 Negotiate and Kerberos V5 need a fake user name

 In order to get Negotiate (SPNEGO) authentication to work in HTTP or Kerberos
 V5 in the email protocols, you need to  provide a (fake) user name (this
 concerns both curl and the lib) because the code wrongly only considers
 authentication if there's a user name provided by setting
 conn->bits.user_passwd in url.c  https://curl.se/bug/view.cgi?id=440 How?
 https://curl.se/mail/lib-2004-08/0182.html A possible solution is to
 either modify this variable to be set or introduce a variable such as
 new conn->bits.want_authentication which is set when any of the authentication
 options are set.

6.5 NTLM does not support password with § character

 https://github.com/curl/curl/issues/2120

6.6 libcurl can fail to try alternatives with --proxy-any

 When connecting via a proxy using --proxy-any, a failure to establish an
 authentication will cause libcurl to abort trying other options if the
 failed method has a higher preference than the alternatives. As an example,
 --proxy-any against a proxy which advertise Negotiate and NTLM, but which
 fails to set up Kerberos authentication will not proceed to try authentication
 using NTLM.

 https://github.com/curl/curl/issues/876

6.7 Do not clear digest for single realm

 https://github.com/curl/curl/issues/3267

6.9 SHA-256 digest not supported in Windows SSPI builds

 Windows builds of curl that have SSPI enabled use the native Windows API calls
 to create authentication strings. The call to InitializeSecurityContext fails
 with SEC_E_QOP_NOT_SUPPORTED which causes curl to fail with CURLE_AUTH_ERROR.

 Microsoft does not document supported digest algorithms and that SEC_E error
 code is not a documented error for InitializeSecurityContext (digest).

 https://github.com/curl/curl/issues/6302

6.10 curl never completes Negotiate over HTTP

 Apparently it is not working correctly...?

 See https://github.com/curl/curl/issues/5235

6.11 Negotiate on Windows fails

 When using --negotiate (or NTLM) with curl on Windows, SSL/TLS handshake
 fails despite having a valid kerberos ticket cached. Works without any issue
 in Unix/Linux.

 https://github.com/curl/curl/issues/5881

6.12 cannot use Secure Transport with Crypto Token Kit

 https://github.com/curl/curl/issues/7048

6.13 Negotiate authentication against Hadoop HDFS

 https://github.com/curl/curl/issues/8264

7. FTP

7.3 FTP with NOBODY and FAILONERROR

 It seems sensible to be able to use CURLOPT_NOBODY and CURLOPT_FAILONERROR
 with FTP to detect if a file exists or not, but it is not working:
 https://curl.se/mail/lib-2008-07/0295.html

7.4 FTP with ACCT

 When doing an operation over FTP that requires the ACCT command (but not when
 logging in), the operation will fail since libcurl does not detect this and
 thus fails to issue the correct command:
 https://curl.se/bug/view.cgi?id=635

7.11 FTPS upload data loss with TLS 1.3

 During FTPS upload curl does not attempt to read TLS handshake messages sent
 after the initial handshake. OpenSSL servers running TLS 1.3 may send such a
 message. When curl closes the upload connection if unread data has been
 received (such as a TLS handshake message) then the TCP protocol sends an
 RST to the server, which may cause the server to discard or truncate the
 upload if it has not read all sent data yet, and then return an error to curl
 on the control channel connection.

 Since 7.78.0 this is mostly fixed. curl will do a single read before closing
 TLS connections (which causes the TLS library to read handshake messages),
 however there is still possibility of an RST if more messages need to be read
 or a message arrives after the read but before close (network race condition).

 https://github.com/curl/curl/issues/6149

7.12 FTPS directory listing hangs on Windows with Schannel

 https://github.com/curl/curl/issues/9161

9. SFTP and SCP

9.1 SFTP does not do CURLOPT_POSTQUOTE correct

 When libcurl sends CURLOPT_POSTQUOTE commands when connected to a SFTP server
 using the multi interface, the commands are not being sent correctly and
 instead the connection is "cancelled" (the operation is considered done)
 prematurely. There is a half-baked (busy-looping) patch provided in the bug
 report but it cannot be accepted as-is. See
 https://curl.se/bug/view.cgi?id=748

9.2 wolfssh: publickey auth does not work

 When building curl to use the wolfSSH backend for SFTP, the publickey
 authentication does not work. This is simply functionality not written for curl
 yet, the necessary API for make this work is provided by wolfSSH.

 See https://github.com/curl/curl/issues/4820

9.3 Remote recursive folder creation with SFTP

 On this servers, the curl fails to create directories on the remote server
 even when the CURLOPT_FTP_CREATE_MISSING_DIRS option is set.

 See https://github.com/curl/curl/issues/5204

9.4 libssh blocking and infinite loop problem

 In the SSH_SFTP_INIT state for libssh, the ssh session working mode is set to
 blocking mode. If the network is suddenly disconnected during sftp
 transmission, curl will be stuck, even if curl is configured with a timeout.

 https://github.com/curl/curl/issues/8632


10. SOCKS

10.3 FTPS over SOCKS

 libcurl does not support FTPS over a SOCKS proxy.


11. Internals

11.2 error buffer not set if connection to multiple addresses fails

 If you ask libcurl to resolve a hostname like example.com to IPv6 addresses
 only. But you only have IPv4 connectivity. libcurl will correctly fail with
 CURLE_COULDNT_CONNECT. But the error buffer set by CURLOPT_ERRORBUFFER
 remains empty. Issue: https://github.com/curl/curl/issues/544

11.4 HTTP test server 'connection-monitor' problems

 The 'connection-monitor' feature of the sws HTTP test server does not work
 properly if some tests are run in unexpected order. Like 1509 and then 1525.

 See https://github.com/curl/curl/issues/868

11.5 Connection information when using TCP Fast Open

 CURLINFO_LOCAL_PORT (and possibly a few other) fails when TCP Fast Open is
 enabled.

 See https://github.com/curl/curl/issues/1332 and
 https://github.com/curl/curl/issues/4296

11.7 signal-based resolver timeouts

 libcurl built without an asynchronous resolver library uses alarm() to time
 out DNS lookups. When a timeout occurs, this causes libcurl to jump from the
 signal handler back into the library with a sigsetjmp, which effectively
 causes libcurl to continue running within the signal handler. This is
 non-portable and could cause problems on some platforms. A discussion on the
 problem is available at https://curl.se/mail/lib-2008-09/0197.html

 Also, alarm() provides timeout resolution only to the nearest second. alarm
 ought to be replaced by setitimer on systems that support it.

11.16 libcurl uses renames instead of locking for atomic operations

 For saving cookies, alt-svc and hsts files. This is bad when for example the
 file is stored in a directory where the application has no write permission
 but it has permission for the file.

 https://github.com/curl/curl/issues/6882
 https://github.com/curl/curl/pull/6884

12. LDAP

12.1 OpenLDAP hangs after returning results

 By configuration defaults, OpenLDAP automatically chase referrals on
 secondary socket descriptors. The OpenLDAP backend is asynchronous and thus
 should monitor all socket descriptors involved. Currently, these secondary
 descriptors are not monitored, causing OpenLDAP library to never receive
 data from them.

 As a temporary workaround, disable referrals chasing by configuration.

 The fix is not easy: proper automatic referrals chasing requires a
 synchronous bind callback and monitoring an arbitrary number of socket
 descriptors for a single easy handle (currently limited to 5).

 Generic LDAP is synchronous: OK.

 See https://github.com/curl/curl/issues/622 and
     https://curl.se/mail/lib-2016-01/0101.html

12.2 LDAP on Windows does authentication wrong?

 https://github.com/curl/curl/issues/3116

12.3 LDAP on Windows does not work

 A simple curl command line getting "ldap://ldap.forumsys.com" returns an
 error that says "no memory" !

 https://github.com/curl/curl/issues/4261

12.4 LDAPS with NSS is slow

 See https://github.com/curl/curl/issues/5874

13. TCP/IP

13.2 Trying local ports fails on Windows

 This makes '--local-port [range]' to not work since curl can't properly
 detect if a port is already in use, so it'll try the first port, use that and
 then subsequently fail anyway if that was actually in use.

 https://github.com/curl/curl/issues/8112

15. CMake

15.2 support build with GnuTLS

15.3 unusable tool_hugehelp.c with MinGW

 see https://github.com/curl/curl/issues/3125

15.4 build docs/curl.1

 The cmake build does not create the docs/curl.1 file and therefore must rely on
 it being there already. This makes the --manual option not work and test
 cases like 1139 cannot function.

15.6 uses -lpthread instead of Threads::Threads

 See https://github.com/curl/curl/issues/6166

15.7 generated .pc file contains strange entries

 The Libs.private field of the generated .pc file contains -lgcc -lgcc_s -lc
 -lgcc -lgcc_s

 See https://github.com/curl/curl/issues/6167

15.8 libcurl.pc uses absolute library paths

 The libcurl.pc file generated by cmake contains things like Libs.private:
 /usr/lib64/libssl.so /usr/lib64/libcrypto.so /usr/lib64/libz.so. The
 autotools equivalent would say Libs.private: -lssl -lcrypto -lz

 See https://github.com/curl/curl/issues/6169

15.11 ExternalProject_Add does not set CURL_CA_PATH

 CURL_CA_BUNDLE and CURL_CA_PATH are not set properly when cmake's
 ExternalProject_Add is used to build curl as a dependency.

 See https://github.com/curl/curl/issues/6313

15.13 CMake build with MIT Kerberos does not work

 Minimum CMake version was bumped in curl 7.71.0 (#5358) Since CMake 3.2
 try_compile started respecting the CMAKE_EXE_FLAGS. The code dealing with
 MIT Kerberos detection sets few variables to potentially weird mix of space,
 and ;-separated flags. It had to blow up at some point. All the CMake checks
 that involve compilation are doomed from that point, the configured tree
 cannot be built.

 https://github.com/curl/curl/issues/6904

16. Applications

17. HTTP/2

17.2 HTTP/2 frames while in the connection pool kill reuse

 If the server sends HTTP/2 frames (like for example an HTTP/2 PING frame) to
 curl while the connection is held in curl's connection pool, the socket will
 be found readable when considered for reuse and that makes curl think it is
 dead and then it will be closed and a new connection gets created instead.

 This is *best* fixed by adding monitoring to connections while they are kept
 in the pool so that pings can be responded to appropriately.

17.3 ENHANCE_YOUR_CALM causes infinite retries

 Infinite retries with 2 parallel requests on one connection receiving GOAWAY
 with ENHANCE_YOUR_CALM error code.

 See https://github.com/curl/curl/issues/5119

18. HTTP/3

18.1 connection migration does not work

 https://github.com/curl/curl/issues/7695