CVE-2026-42791: Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP

Routine

LOW 3.7REMOTEUPGRADE

CVE-2026-42791 is a low-severity flaw (CVSS 3.7) affecting erlang\/otp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtaine

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	3.7 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 76%)
CISA exploited list	No
Weakness	CWE-295, CWE-672
Published	2026-05-27
Last modified	2026-10-26

Publisher (CNA): EEF · Vendor: erlang

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-27 14:16 UTCPublished CVE record published
2026-10-26 11:10 UTCUpdated Record last modified

erlang erlang\/otp UPGRADE

Affected: >= 27.0 and < 27.3.4.12 · >= 28.0 and < 28.5.0.1 · >= 29.0 and < 29.0.1

Fixed in: 27.3.4.12, 28.5.0.1, 29.0.1

Safe to downgrade to: a release before 27.0

1. Check installed version

apt-cache policy erlangotp || rpm -q erlangotp || erlangotp --version

2. UPGRADE to 27.3.4.12 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade erlangotp

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade erlangotp

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 27.0 (Debian / Ubuntu)

apt-cache madison erlangotp sudo apt install erlangotp=<VERSION_BEFORE_27.0> sudo apt-mark hold erlangotp

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list erlangotp sudo dnf downgrade erlangotp-<VERSION_BEFORE_27.0> sudo dnf versionlock add erlangotp

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42791?

erlang\/otp: upgrade to 27.3.4.12, 28.5.0.1, 29.0.1. Exact commands for each OS are on this page.

Is CVE-2026-42791 being exploited?

CVE-2026-42791 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42791 affect?

CVE-2026-42791 affects erlang\/otp. Severity is low (CVSS 3.7). Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify

How urgent is CVE-2026-42791?

Priority 24/100. Remotely exploitable, no login, no user action

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References

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