Cyber Resilience

CVE-2026-55953

Erlang\/Otp 17.0 – 27.3.4.15

Published
27 July 2026
Modified
10 August 2026
Patch / advisory
View advisory
CVSS Score v4 9.1
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0021 12th percentile
Risk Priority 44 floored blend · peak EPSS

Summary

CVE-2026-55953 is a critical-severity Algorithm Downgrade (CWE-757) vulnerability in Erlang Erlang\/Otp. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Downgrade Attack (T1689); ranked at the 12th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SC-13 (Cryptographic Protection) and SC-8 (Transmission Confidentiality and Integrity) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A04:2025 Cryptographic Failures

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-757

Related Threats

MITRE ATT&CK Enterprise Techniques

T1689 Downgrade Attack Defense Impairment
Adversaries may downgrade or use a version of system features that may be outdated, vulnerable, and/or does not support updated security controls.
attack.mitre.org →
T1600 Weaken Encryption Defense Impairment
Adversaries may compromise a network device’s encryption capability in order to bypass encryption that would otherwise protect data communications.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-48860Same product: Erlang Erlang\/Otp
CVE-2026-55950Same product: Erlang Erlang\/Otp
CVE-2026-54891Same product: Erlang Erlang\/Otp
CVE-2026-54887Same product: Erlang Erlang\/Otp
CVE-2026-58227Same product: Erlang Erlang\/Otp
CVE-2026-55952Same product: Erlang Erlang\/Otp
CVE-2026-32144Same product: Erlang Erlang\/Otp
CVE-2026-42790Same product: Erlang Erlang\/Otp
CVE-2026-42789Same product: Erlang Erlang\/Otp
CVE-2026-42791Same product: Erlang Erlang\/Otp

Affected Assets

erlang
erlang\/otp
17.0 — 27.3.4.15 · 28.0 — 28.5.0.4 · 29.0 — 29.0.4
erlang
erlang\/ssl
5.3.4 — 11.2.12.11 · 11.3 — 11.6.0.4 · 11.7 — 11.7.4

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 7 hardening rules · 5 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V12.1.1
  • V12.2.1
  • V12.3.3
  • V17.2.2

Mitigating Controls (NIST 800-53 r5) AI

SC-13 Cryptographic Protection good match

Specifying and implementing required cryptography types directly precludes negotiation or acceptance of weaker algorithms.

SC-8 Transmission Confidentiality and Integrity partial match

Requiring protection of transmitted confidentiality and integrity forces selection of sufficiently strong negotiated algorithms rather than weaker ones.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-04 none match
prevents

PR.AA-04 addresses protection/verification of identity assertions in SSO/federation contexts while CWE-757 concerns protocol-level crypto algorithm negotiation, so the control neither prevents nor meaningfully mitigates the weakness.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect and block algorithm downgrade vulnerabilities before deployment.

A.8.21 Security of network services partial match
mitigates

Ensures network services use secure cryptographic parameters, reducing downgrade risk.

A.8.24 Use of cryptography partial match
prevents

Mandates use of strong, approved cryptographic algorithms, directly preventing downgrade to weaker ones.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC practices include selecting strong crypto algorithms during design and implementation.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify minimum cryptographic strength to avoid downgrades.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include enforcing strong algorithm selection in protocol design.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Windows 10 (1 rule)
  • V-220938 The LanMan authentication level must be set to send NTLMv2 response only, and to refuse LM and NTLM. prevents CWE-757
Windows 11 (1 rule)
  • V-253462 The LanMan authentication level must be set to send NTLMv2 response only, and to refuse LM and NTLM. prevents CWE-757
Windows Server 2016 (1 rule)
  • V-225054 The LAN Manager authentication level must be set to send NTLMv2 response only and to refuse LM and NTLM. prevents CWE-757
Windows Server 2019 (1 rule)
  • V-205919 Windows Server 2019 LAN Manager authentication level must be configured to send NTLMv2 response only and to refuse LM and NTLM. prevents CWE-757
Windows Server 2022 (1 rule)
  • V-254475 Windows Server 2022 LAN Manager authentication level must be configured to send NTLMv2 response only and to refuse LM and NTLM. prevents CWE-757

References