CriticalCVE-2026-55953

    TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication (CVE-2026-55953)

    Published Last modified Sources: Ubuntu, Red Hat, SUSE, Debian, BSI, Msrc Update Guide, OSV, CVE.org

    What is affected, what to do

    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.

    Update Erlang OTP to version 27.3.4.15, Erlang OTP to version 28.5.0.4, Erlang OTP to version 29.0.4.

    Affected
    • Erlang OTP lt 17.0..27.3.4.15
    • Erlang OTP lt 28.0..28.5.0.4
    • Erlang OTP lt 29.0..29.0.4
    • Erlang OTP lt 5.3.4..11.2.12.11
    • Erlang OTP lt 11.3..11.6.0.4
    • Erlang OTP lt 11.7..11.7.4
    Fixed in
    • Erlang OTP 27.3.4.15
    • Erlang OTP 28.5.0.4
    • Erlang OTP 29.0.4
    • Erlang OTP 11.2.12.11
    • Erlang OTP 11.6.0.4
    • Erlang OTP 11.7.4

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.1

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v4

    7.4

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Ubuntu, Red Hat, SUSE, Debian, BSI, Msrc Update Guide, OSV, CVE.org

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 14.3

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    68.81 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.1 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.4
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.1
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.2 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    14.3
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 27 July 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-757

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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: Ubuntu Security Notices, redhat_csaf, suse_csaf, Debian Security Advisories, BSI WID Portal, BSI CSAF, Microsoft Security Update Guide, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    ErlangOTP
    • 11.3 – < 11.6.0.4
    • 11.7 – < 11.7.4
    • 28.0 – < 28.5.0.4
    • 29.0 – < 29.0.4
    • 17.0 – < 27.3.4.15
    • 5.3.4 – < 11.2.12.11
    • 11.6.0.4
    • 11.7.4
    • 28.5.0.4
    • 29.0.4
    • 27.3.4.15
    • 11.2.12.11
    erlangerlang\/otp
    • 17.0 – < 27.3.4.15
    • 28.0 – < 28.5.0.4
    • 29.0 – < 29.0.4
    • 27.3.4.15
    • 28.5.0.4
    • 29.0.4
    erlangerlang\/ssl
    • 11.7 – < 11.7.4
    • 5.3.4 – < 11.2.12.11
    • 11.3 – < 11.6.0.4
    • 11.7.4
    • 11.2.12.11
    • 11.6.0.4
    Open SourceErlang/OTP
    • < 28.5.0.4
    • < 27.3.4.15
    • < 29.0.4
    • 28.5.0.4
    • 27.3.4.15
    • 29.0.4

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianerlangtrixie
    Linuxubuntuerlangbionic
    Linuxubuntuerlangfocal
    Linuxubuntuerlangjammy
    Linuxubuntuerlangnoble
    Linuxubuntuerlangresolute
    Linuxubuntuerlangtrusty
    Linuxubuntuerlangxenial

    Weakness classes (CWE)

    • CWE-757Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')

      Base

      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 algorithm that is available to both parties.

      Entry at MITRE CWE-757

    References & sources

    • github.comerlang/otp/security/advisories/GHSA-c6cw-pr89-w882advisory, Vendor advisory, related, Vendor advisory
    • cna.erlef.orgcves/CVE-2026-55953.htmlweb, related, Patch, Third-party advisory
    • erlang.orgdoc/system/versions.htmlweb, x_version-scheme, Release notes
    • github.comerlang/otp/commit/064e236414614f9085cbbbd6eacf0e43c02d1b4bfix, Patch, Patch
    • github.comerlang/otp/commit/0a82596d425abe43dc2e0b3d74aa1557ef74051cfix, Patch, Patch
    • github.comerlang/otp/commit/e6ff938116b2872bccc478af7fefb56627285b77fix, Patch, Patch
    • OSV (Open Source Vulnerabilities)vulnerability/EEF-CVE-2026-55953related, Patch, Third-party advisory

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedEEF

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/55xxx/CVE-2026-55953.json">CVE-2026-55953</a>

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

    2. Initial analysis by NVDNVD

      Newly listed as affected:
      • erlang/otp (28.0 – before 28.5.0.4; 29.0 – before 29.0.4; 17.0 – before 27.3.4.15)
      • erlang/ssl (11.3 – before 11.6.0.4; 11.7 – before 11.7.4; 5.3.4 – before 11.2.12.11)

      CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
      Product configurationadded
      —
      OR *cpe:2.3:a:erlang:erlang/otp:*:*:*:*:*:*:*:* versions from (including) 28.0 up to (excluding) 28.5.0.4 *cpe:2.3:a:erlang:erlang/otp:*:*:*:*:*:*:*:* versions from (including) 29.0 up to (excluding) 29.0.4 *cpe:2.3:a:erlang:erlang/ssl:*:*:*:*:*:*:*:* versions from (including) 11.3 up to (excluding) 11.6.0.4 *cpe:2.3:a:erlang:erlang/ssl:*:*:*:*:*:*:*:* versions from (including) 11.7 up to (excluding) 11.7.4 *cpe:2.3:a:erlang:erlang/otp:*:*:*:*:*:*:*:* versions from (including) 17.0 up to (excluding) 27.3.4.15 *cpe:2.3:a:erlang:erlang/ssl:*:*:*:*:*:*:*:* versions from (including) 5.3.4 up to (excluding) 11.2.12.11
      Reference typeadded
      —
      EEF: https://cna.erlef.org/cves/CVE-2026-55953.html Types: Patch, Third Party Advisory
      Reference typeadded
      —
      EEF: https://github.com/erlang/otp/commit/064e236414614f9085cbbbd6eacf0e43c02d1b4b Types: Patch
      Reference typeadded
      —
      EEF: https://github.com/erlang/otp/commit/0a82596d425abe43dc2e0b3d74aa1557ef74051c Types: Patch
      Reference typeadded
      —
      EEF: https://github.com/erlang/otp/commit/e6ff938116b2872bccc478af7fefb56627285b77 Types: Patch
      Reference typeadded
      —
      EEF: https://github.com/erlang/otp/security/advisories/GHSA-c6cw-pr89-w882 Types: Vendor Advisory
      Reference typeadded
      —
      EEF: https://osv.dev/vulnerability/EEF-CVE-2026-55953 Types: Patch, Third Party Advisory
      Reference typeadded
      —
      EEF: https://www.erlang.org/doc/system/versions.html#order-of-versions Types: Release Notes

      Source identifier: nvd@nist.gov

    3. Record modifiedEEF

      Description added or changed

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)changed
      OTP, OTP
      OTP, OTP, OTP
      Descriptionchanged
      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 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15, corresponding to ssl from 5.3.4 before 11.7.4, 11.6.0.4 and 11.2.12.11.
      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.

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

    4. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-55953","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-07-27T18:33:59.966358Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    5. ReceivedEEF

      CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

      Weakness type: CWE-757

      Description added or changed

      Show 11 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      OTP, OTP
      Descriptionadded
      —
      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 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15, corresponding to ssl from 5.3.4 before 11.7.4, 11.6.0.4 and 11.2.12.11.
      CVSSadded
      —
      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
      Weakness type (CWE)added
      —
      CWE-757
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-55953.html
      Referenceadded
      —
      https://github.com/erlang/otp/commit/064e236414614f9085cbbbd6eacf0e43c02d1b4b
      Referenceadded
      —
      https://github.com/erlang/otp/commit/0a82596d425abe43dc2e0b3d74aa1557ef74051c
      Referenceadded
      —
      https://github.com/erlang/otp/commit/e6ff938116b2872bccc478af7fefb56627285b77
      Referenceadded
      —
      https://github.com/erlang/otp/security/advisories/GHSA-c6cw-pr89-w882
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-55953
      Referenceadded
      —
      https://www.erlang.org/doc/system/versions.html#order-of-versions

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

    One NVD translation into another language is hidden.

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2026-55953
    <a href="https://intel.neosec.eu/en/cve/CVE-2026-55953"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-55953.svg?lang=en" alt="CVE-2026-55953 – NEOSEC Intel" height="20"></a>