CyberSecBulletin
CVE-2026-55953NVD status: Modified

OTP: Selection of Less-Secure Algorithm During Negotiation

Published Updated By the CyberSecBulletin desk

CVE-2026-55953 is a high-severity selection of less-secure algorithm during negotiation vulnerability in OTP from Erlang, with a CVSS 3.1 base score of 7.4 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 27.3.4.15, 28.5.0.4, 29.0.4 as the first without the flaw, so updating OTP to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.23% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update OTP to 27.3.4.15 or 28.5.0.4 or 29.0.4 or 11.2.12.11, whichever matches your release line, or a later version.
  2. Update Erlang/otp to 27.3.4.15 or 28.5.0.4 or 29.0.4, whichever matches your release line, or a later version.
  3. Update Erlang/ssl to 11.2.12.11 or 11.6.0.4 or 11.7.4, whichever matches your release line, or a later version.
  4. Read the advisory on github.com for workarounds and exact fixed builds.
  5. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
ErlangOTP17.0 up to, but not including, 27.3.4.15; 28.0 up to, but not including, 28.5.0.4; 29.0 up to, but not including, 29.0.4; 5.3.4 up to, but not including, 11.2.12.11; 11.3 up to, but not including, 11.6.0.4; 11.7 up to, but not including, 11.7.4; 84adefa331c4159d432d22840663c38f155cd4c1 and later27.3.4.15, 28.5.0.4, 29.0.4, 11.2.12.11, 11.6.0.4, 11.7.4
ErlangErlang/otp17.0 up to, but not including, 27.3.4.15; 28.0 up to, but not including, 28.5.0.4; 29.0 up to, but not including, 29.0.427.3.4.15, 28.5.0.4, 29.0.4
ErlangErlang/ssl5.3.4 up to, but not including, 11.2.12.11; 11.3 up to, but not including, 11.6.0.4; 11.7 up to, but not including, 11.7.411.2.12.11, 11.6.0.4, 11.7.4

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
HighSuccess depends on conditions outside the attacker's control.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
NoneAvailability is not affected.

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 4.09.1CriticalCNA
CVSS 3.17.4HighNVD

Official 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 17.0 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 5.3.4 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 17.0, corresponding to ssl before 5.3.4, is affected is unknown.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Selection of Less-Secure Algorithm During Negotiation

A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used in a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.

More Selection of Less-Secure Algorithm During Negotiation vulnerabilities (CWE-757)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in OTP

All OTP vulnerabilities

Recent Selection of Less-Secure Algorithm During Negotiation vulnerabilities

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