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VulnerabilityPublished Updated

CVE-2026-42790: Erlang OTP · Improper Certificate Validation

Affects Erlang OTPSource CVE Database V5

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Not known to be exploited · CVSS 7.6 High : upgrade to 1.15.1.7 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 4.0 base score
7.6High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.15.1.7, 26.2.5.21
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade OTP and public_key to 1.15.1.7; OTP and erlang/otp to 26.2.5.21.

Affected software

ProductAffectedFixed in
ErlangOTPAffected
  • >=1.4 <1.15.1.7
Fixed in
  • 1.15.1.7
ErlangOTPAffected
  • >=19.3 <26.2.5.21
Fixed in
  • 26.2.5.21
GitHuberlang/otppkg:github/erlang/otpOther threatsAffected
  • =1.4
Fixed in–
GitHubpublic_keypkg:github/public_keyOther threatsAffected
  • >=1.4 <1.15.1.7
Fixed in
  • 1.15.1.7
GitHuberlang/otppkg:github/erlang/otpOther threatsAffected
  • >=19.3 <26.2.5.21
Fixed in
  • 26.2.5.21

CPE configurations (1)

  • cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available and should be applied. Vendors including Red Hat have released patched versions addressing this issue. As an immediate mitigation, ensure all TLS certificates include Subject Alternative Name (SAN) extensions with appropriate DNS entries, avoiding reliance on the CommonName (CN) field for hostname verification. Erlang applications can configure the ssl module's verify_fun option to reject peer certificates missing the subjectAltName extension. Users should apply vendor patches promptly and follow vendor-specific update instructions.

Description

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a DNS nameConstraints bypass via subject CommonName fallback in TLS hostname verification. Two flaws combine to allow a subordinate CA whose DNS nameConstraints are restricted (e.g. permitted;DNS:allowed.example.com) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. victim.example.com): First, pubkey_cert:validate_names/6 in lib/public_key/src/pubkey_cert.erl only checks SAN DNS entries against nameConstraints. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no subjectAltName therefore trivially satisfies any permitted;DNS:... constraint regardless of its subject commonName. Second, public_key:pkix_verify_hostname/3 in lib/public_key/src/public_key.erl falls back to the subject commonName when no subjectAltName is present, extracting id-at-commonName attributes as presented IDs and matching them against the reference hostname. The strict pkix_verify_hostname_match_fun(https) matcher does not suppress this fallback. The result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the nameConstraints are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock ssl:connect with verify_peer, a trusted CA, SNI, and the canonical strict https hostname matcher. This issue affects OTP from OTP 19.3 before OTP 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 1.4 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.

References

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