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Erlang/OTP TLS 1.3 PSK List Validation Denial of Service
CVE-2026-55952 is a denial-of-service vulnerability in the Erlang/OTP ssl application's processing of TLS 1.3 pre-shared key extensions. The function tls_handshake_1_3:handle_pre_shared_key/3 does not verify that the PSK identity and binder lists have equal lengths before forwarding an OfferedPreSharedKeys record to tls_server_session_ticket:use/4. A single ClientHello containing mismatched lists can crash the session ticket handler on a listener with session tickets enabled, in either stateful or stateless mode. Subsequent TLS 1.3 connections fail when the server attempts to issue session tickets. Affected releases begin at OTP 22.2, corresponding to ssl 9.5; fixed releases are OTP 29.0.3, 28.5.0.3, and 27.3.4.14, corresponding respectively to ssl 11.7.3, 11.6.0.3, and 11.2.12.10.
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 causes persistent loss of TLS 1.3 availability on the affected listener. New TLS 1.3 handshakes can complete, but their connection processes subsequently crash when issuing session tickets, effectively preventing usable TLS 1.3 connections until the ssl application is restarted. TLS 1.2 connections are unaffected. No confidentiality or integrity impact is established.
If you can’t patch tonight, do this now.
Until patched, disable TLS 1.3 session tickets on exposed listeners where operationally feasible, since both stateful and stateless ticket modes are vulnerable. Alternatively, temporarily disable TLS 1.3 while retaining TLS 1.2 where security policy permits, or restrict listener access to trusted networks. Restarting the ssl application restores service after exploitation but does not prevent another attack.
Patch, then assume compromise.
Upgrade to OTP 29.0.3, 28.5.0.3, or 27.3.4.14, or a later patched release in the applicable branch. The corresponding fixed ssl versions are 11.7.3, 11.6.0.3, and 11.2.12.10. Distribution-managed installations should apply the vendor's corrected Erlang packages; Debian trixie provides the fix in erlang version 1:27.3.4.1+dfsg-1+deb13u3 or later. Restart the ssl application after updating and verify TLS 1.3 connection establishment and session ticket issuance.
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.
16 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.