Docs Overview
Project
Bug Bounty Bug Report Code of conduct Dependencies Donate FAQ Features Governance History Install Known Bugs Logo TODO website Info
Protocols
CA Extract HTTP cookies HTTP/3 MQTT SSL certs SSL libs compared URL syntax WebSocket
Releases
Changelog curl CVEs Release Table Version Numbering Vulnerabilities
Tool
Comparison Table curl man page HTTP Scripting mk-ca-bundle Tutorial When options were added
Who and Why
Companies Copyright Sponsors Thanks The name
curl / Docs / curl CVEs / TLS session resumption client cert bypass (again)
Related:
Audits
Bug Bounty
Changelog
curl CVEs
JSON metadata
Vulnerability Disclosure
Vulnerabilities Table

CVE-2017-7468

TLS session resumption client cert bypass (again)

Project curl Security Advisory, April 19th 2017 - Permalink

VULNERABILITY

libcurl would attempt to resume a TLS session even if the client certificate had changed. That is unacceptable since a server by specification is allowed to skip the client certificate check on resume, and may instead use the old identity which was established by the previous certificate (or no certificate).

libcurl supports by default the use of TLS session id/ticket to resume previous TLS sessions to speed up subsequent TLS handshakes. They are used when for any reason an existing TLS connection could not be kept alive to make the next handshake faster.

This flaw is a regression and identical to CVE-2016-5419 reported on August 3rd 2016, but affecting a different version range.

INFO

This flaw also affects the curl command line tool.

For version 7.52.0, we rearranged a lot of TLS code to bring support for HTTPS proxies, which unfortunately made us accidentally bring this old flaw back!

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2017-7468 to this issue.

CWE-305: Authentication Bypass by Primary Weakness

Severity: High

AFFECTED VERSIONS

This flaw is relevant for all versions of curl and libcurl that support TLS and client certificates.

libcurl is used by many applications, but not always advertised as such!

SOLUTION

TLS session resumption is disabled when a client certificate is used so that a subsequent connection attempt to the same server cannot risk getting a previously authenticated session resumed.

RECOMMENDATIONS

We suggest you take one of the following actions immediately, in order of preference:

A - Upgrade curl and libcurl to version 7.54.0

B - Apply the patch to your version and rebuild

C - Set CURLOPT_SSL_SESSIONID_CACHE to 0L when using client certificates

TIMELINE

It was first reported to the curl project on March 21, 2017. We contacted distros@openwall on April 10.

libcurl 7.54.0 was released on April 19 2017, coordinated with the publication of this advisory.

CREDITS

Thanks a lot!