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OpenSSL TLS 1.2 Hash Selection Denial of Service
CVE-2013-6449 is a denial-of-service vulnerability in OpenSSL's TLS 1.2 handshake processing. The ssl_get_algorithm2 function retrieves a protocol version number from an incorrect data structure, potentially selecting an inappropriate hashing algorithm. Subsequent digest processing can encounter a null digest pointer and crash the application. A remote attacker can trigger the flaw using crafted traffic from a TLS 1.2 client. The issue affects vulnerable OpenSSL 1.0.1 releases and was fixed in 1.0.1f. OpenSSL 0.9.8 does not experience the security impact because it lacks TLS 1.2 support.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Successful exploitation can terminate an OpenSSL-based daemon or application, interrupting established connections and making the affected service unavailable. Repeated triggering may cause recurring outages. No confidentiality or integrity impact, arbitrary code execution, or privilege escalation is established for this vulnerability.
If you can’t patch tonight, do this now.
Temporarily disabling TLS 1.2 prevented the observed Apache Traffic Server crashes. This is a historical workaround, not a suitable long-term replacement for patching, because falling back to obsolete protocol versions introduces other security risks. Where patching is delayed, restrict access to affected services or disable unnecessary exposed services.
Patch, then assume compromise.
Install an OpenSSL release containing the fix, introduced upstream in 1.0.1f, or an applicable vendor-backported update. Historical fixed packages include Red Hat Enterprise Linux 6 OpenSSL 1.0.1e-16.el6_5.4 and Debian wheezy OpenSSL 1.0.1e-2+deb7u1. Restart every service linked to OpenSSL, or reboot the system, to load the corrected library. Because OpenSSL 1.0.1 is unsupported, use a currently supported release rather than treating the historical minimum fixed version as a suitable deployment target.
No public exploits tracked yet. Mallory keeps watching.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
19 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.