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🛡️ CVE-2026-55953 on Debian — erlang

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

The Erlang/OTP ssl TLS 1.2 (and earlier) and DTLS client does not verify that the cipher suite selected by the server in ServerHello was among the suites offered by the client in ClientHello. The client-side tls_handshake:hello/5 handler validates the negotiated protocol version and the downgrade sentinel but hands the server-chosen suite directly to ssl_handshake:handle_server_hello_extensions/9, which installs it without a membership check. The TLS 1.3 client path performs this check (per RFC 8446), so it is not affected. An on-path attacker between the client and the intended server can respond with a ServerHello selecting an anonymous key exchange suite such as TLS_DH_anon_* or TLS_ECDH_anon_* that the client never offered. Anonymous suites do not require the server to present a certificate, so the entire verify_peer and cacerts configuration is bypassed: the attacker completes the handshake with its own ephemeral parameters, no certificate is validated, no hostname is checked, and ssl:connect returns {ok, Socket}. All subsequent application traffic is readable and modifiable by the attacker. This issue affects OTP from OTP R13B03 before OTP 27.3.4.15, from OTP 28.0 before OTP 28.5.0.4, and from OTP 29.0 before OTP 29.0.4, corresponding to ssl from 3.10.7 before 11.2.12.11, from 11.3 before 11.6.0.4, and from 11.7 before 11.7.4. Whether OTP before OTP R13B03, corresponding to ssl before 3.10.7, is affected is unknown.

Distribution advisory

This page covers CVE-2026-55953 as tracked by Debian, for the package erlang. The fix is available in version 1:29.0.4+dfsg-1; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: None.

Weakness class

DEBIAN-CVE-2026-55953 is classified as CWE-757: Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade'). A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest…

Affected software

DEBIAN-CVE-2026-55953 is recorded against 1 package.

  • erlang (fixed in 1:29.0.4+dfsg-1)

Timeline and source

Published on 27 July 2026 and last revised on 11 August 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

security-tracker.debian.org (Advisory)

Other advisories for this package

erlang has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-757: Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')) in other software:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-07-27
Updated 2026-08-20
Modified 2026-08-11
Fix URL N/A

Affected Packages

Software From version Fixed in
erlang — 1:29.0.4+dfsg-1

Similar Threats

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