CVE-2026-42790Network attack vector

TLS host impersonation via CommonName fallback

Published May 27, 2026 · Updated May 27, 2026

Improper certificate validation in Erlang/OTP public_key allows man-in-the-middle attackers to impersonate out-of-scope TLS hosts. pubkey_cert:validate_names/6 ignores a subject CommonName when enforcing DNS nameConstraints, while public_key:pkix_verify_hostname/3 accepts that CommonName when SAN is absent. Exploitation requires control of a DNS-constrained subordinate CA key and interception of TLS traffic; success exposes data and permits traffic modification under the forged host identity.

CVSS severity7.6
High
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Erlang/OTP public_key allows man-in-the-middle attackers to impersonate out-of-scope TLS hosts. pubkey_cert:validate_names/6 ignores a subject CommonName when enforcing DNS nameConstraints, while public_key:pkix_verify_hostname/3 accepts that CommonName when SAN is absent. Exploitation requires control of a DNS-constrained subordinate CA key and interception of TLS traffic; success exposes data and permits traffic modification under the forged host identity.

The record

CVE
CVE-2026-42790
Published
May 27, 2026
Updated
May 27, 2026
Vendor
Erlang
Product
Erlang/OTP
Classifications
CWE-297, CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2026CVE publishedPublication date reported by the CVE source.
  2. May 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.4 <* changes=[{"at":"1.15.1.7","status":"unaffected"},{"at":"1.17.1.3","status":"unaffected"},{"at":"1.20.3.1","status":"unaffected"},{"at":"1.21.1","status":"unaffected"}]
  2. Affected versionversion=19.3 <* changes=[{"at":"26.2.5.21","status":"unaffected"},{"at":"27.3.4.12","status":"unaffected"},{"at":"28.5.0.1","status":"unaffected"},{"at":"29.0.1","status":"unaffected"}]
  3. Affected versionversion=b0c245e8132bb13171e277b1af59c0cec00c9459 <* changes=[{"at":"0769050c69d73762672b0db1347b6993a5b31759","status":"unaffected"},{"at":"fb67c6d1836f51105a96d8b769e71e4215a79457","status":"unaffected"},{"at":"21abed64eb2026b5f82f432709e4e932f9be389a","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Erlang · Erlang/OTPversion=1.4 <* changes=[{"at":"1.15.1.7","status":"unaffected"},{"at":"1.17.1.3","status":"unaffected"},{"at":"1.20.3.1","status":"unaffected"},{"at":"1.21.1","status":"unaffected"}]; version=19.3 <* changes=[{"at":"26.2.5.21","status":"unaffected"},{"at":"27.3.4.12","status":"unaffected"},{"at":"28.5.0.1","status":"unaffected"},{"at":"29.0.1","status":"unaffected"}]; version=b0c245e8132bb13171e277b1af59c0cec00c9459 <* changes=[{"at":"0769050c69d73762672b0db1347b6993a5b31759","status":"unaffected"},{"at":"fb67c6d1836f51105a96d8b769e71e4215a79457","status":"unaffected"},{"at":"21abed64eb2026b5f82f432709e4e932f9be389a","status":"unaffected"}]

Published CVSS scores

7.4Red HatCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
7.6EEFCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-297Improper Validation of Certificate with Host Mismatch
CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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