CVE-2026-55952: TLS 1.3 server denial of service via malformed ClientHello pre-shared key extension
The Erlang/OTP ssl application does not validate that the PSK identity list and binder list carried in a TLS 1.3 ClientHello pre-shared key extension have equal length before passing them to the session ticket handler. In tlshandshake13:handlepresharedkey/3, an OfferedPreSharedKeys record with a mismatched number of identities and binders is forwarded directly to tlsserversessionticket:use/4, which crashes the session ticket handler process.
An unauthenticated remote attacker can send a single crafted ClientHello to a TLS 1.3 server with session tickets enabled (stateful or stateless mode) and permanently disrupt session ticket handling on that listener. New TLS 1.3 handshakes complete but subsequently crash when the server attempts to issue a session ticket, effectively making TLS 1.3 unusable on the affected listener until the ssl application is restarted. TLS 1.2 connections are not affected.
This issue affects OTP from OTP 22.2 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssl from 9.5 before 11.7.3, 11.6.0.3 and 11.2.12.10.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
Disable TLS session tickets on the affected TLS 1.3 listener (session tickets enabled is a required condition for the session ticket handler crash).
- Operational
Restart the ssl application to restore TLS 1.3 session ticket handling on the affected listener after exploitation (TLS 1.3 becomes unusable on that listener until the ssl application is restarted).
Event History
Frequently Asked Questions
What is the severity of CVE-2026-55952?
CVE-2026-55952 has a risk rating of 55, indicating a moderate severity level.
What is CVE-2026-55952 about?
CVE-2026-55952 involves a denial of service vulnerability in TLS 1.3 due to improper validation of pre-shared key extension fields in the Erlang/OTP ssl application.
How do I fix CVE-2026-55952?
To mitigate CVE-2026-55952, users should update their Erlang/OTP installation to the latest version that addresses this vulnerability.
Which software is affected by CVE-2026-55952?
CVE-2026-55952 affects the Erlang OTP and Erlang ssl applications.
What are the potential impacts of CVE-2026-55952?
The impact of CVE-2026-55952 is primarily denial of service, potentially leading to service interruptions for affected users.