Date: Wed, 17 May 2023 08:40:59 +0200 (CEST) From: Daniel Stenberg <daniel@...x.se> To: curl security announcements -- curl users <curl-users@...ts.haxx.se>, curl-announce@...ts.haxx.se, libcurl hacking <curl-library@...ts.haxx.se>, oss-security@...ts.openwall.com Subject: curl: CVE-2023-28319: UAF in SSH sha256 fingerprint check UAF in SSH sha256 fingerprint check ==================================== Project curl Security Advisory, May 17th 2023 - [Permalink](https://curl.se/docs/CVE-2023-28319.html) VULNERABILITY ------------- libcurl offers a feature to verify an SSH server's public key using a SHA 256 hash. When this check fails, libcurl would free the memory for the fingerprint before it returns an error message containing the (now freed) hash. This flaw risks inserting sensitive heap-based data into the error message that might be shown to users or otherwise get leaked and revealed. INFO ---- This only applies to users of the `CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256` option, which is **only supported for libcurl built with libssh2** (curl optionally supports other SSH backends). Either of the options `CURLOPT_VERBOSE` or `CURLOPT_ERRORBUFFER` also need to be set to trigger the problem. The damage is somewhat limited by the extremely short time window between the free and the use of the freed memory. The largest possible info leak that can happen due to this flaw per trigger occasion, is limited to `CURL_ERROR_SIZE` - the error message prefix length (69) = 186 bytes. It will also stop at the first null byte within those 186 bytes. The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2023-28319 to this issue. CWE-416: Use After Free Severity: Medium AFFECTED VERSIONS ----------------- - Affected versions: curl 7.81.0 to and including 8.0.1 - Not affected versions: curl < 7.81.0 and curl >= 8.1.0 - Introduced-in: https://github.com/curl/curl/commit/3467e89bb97e6c87c7 libcurl is used by many applications, but not always advertised as such! SOLUTION ------------ - Fixed-in: https://github.com/curl/curl/commit/8e21b1a05f3c0ee098dbcb6c RECOMMENDATIONS -------------- A - Upgrade curl to version 8.1.0 B - Apply the patch to your local version C - Do not use `CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256` TIMELINE -------- This issue was reported to the curl project on March 21 2023. We contacted distros@...nwall on May 9, 2023. curl 8.1.0 was released on May 17 2023, coordinated with the publication of this advisory. CREDITS ------- - Reported-by: Wei Chong Tan - Patched-by: Daniel Stenberg Thanks a lot! -- / daniel.haxx.se
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