CVE-2026-42789: Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert modul

Routine

MEDIUM 4.8REMOTEUPGRADE

CVE-2026-42789 is a medium-severity flaw (CVSS 4.8) affecting erlang\/otp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery. In lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	4.8 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 68%)
CISA exploited list	No
Weakness	CWE-295, CWE-296
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: >= 17.0 and < 26.2.5.21 · >= 27.0 and < 27.3.4.12 · >= 28.0 and < 28.5.0.1 · >= 29.0 and < 29.0.1

Fixed in: 26.2.5.21, 27.3.4.12, 28.5.0.1, 29.0.1

Safe to downgrade to: a release before 17.0

1. Check installed version

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

2. UPGRADE to 26.2.5.21 (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 17.0 (Debian / Ubuntu)

apt-cache madison erlangotp sudo apt install erlangotp=<VERSION_BEFORE_17.0> 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_17.0> 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-2026-42789?

erlang\/otp: upgrade to 26.2.5.21, 27.3.4.12, 28.5.0.1, 29.0.1. Exact commands for each OS are on this page.

Is CVE-2026-42789 being exploited?

CVE-2026-42789 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-2026-42789 affect?

CVE-2026-42789 affects erlang\/otp. Severity is medium (CVSS 4.8). Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery. In lib/public_key/sr

How urgent is CVE-2026-42789?

Priority 30/100. Remotely exploitable, no login, no user action

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References

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