CVE-2026-91767: php_openssl_matches_wildcard_name() in ext/openssl/xp_ssl.c underflows the length argument passed to memchr()

Routine

MEDIUM 6.5WATCHLISTUPGRADE

CVE-2026-91767 is a medium-severity flaw (CVSS 6.5) affecting php. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

php_openssl_matches_wildcard_name() in ext/openssl/xp_ssl.c underflows the length argument passed to memchr() when a TLS server certificate presents a wildcard name whose literal characters are together longer than the hostname being verified. A malicious server presenting such a certificate makes the PHP client read up to SIZE_MAX bytes past the end of a heap allocation. The path is reachable from any default client stream, because verify_peer_n

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Adjacent network
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.1% (top 99%)
CISA exploited list	No
Weakness	CWE-122
Published	2026-09-25
Last modified	2026-10-27

Publisher (CNA): PHP Group · Vendor: php

Last updated 2026-10-27 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-25 21:17 UTCPublished CVE record published
2026-10-27 13:14 UTCUpdated Record last modified

php php UPGRADE

Affected: >= 8.2.0 and < 8.2.34 · >= 8.3.0 and < 8.3.35 · >= 8.4.0 and < 8.4.26 · >= 8.5.0 and < 8.5.11

Fixed in: 8.2.34, 8.3.35, 8.4.26, 8.5.11

Safe to downgrade to: a release before 8.2.0

1. Check installed version

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

2. UPGRADE to 8.2.34 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade php

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 8.2.0 (Debian / Ubuntu)

apt-cache madison php sudo apt install php=<VERSION_BEFORE_8.2.0> sudo apt-mark hold php

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

dnf --showduplicates list php sudo dnf downgrade php-<VERSION_BEFORE_8.2.0> sudo dnf versionlock add php

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-2026-91767?

php: upgrade to 8.2.34, 8.3.35, 8.4.26, 8.5.11. Exact commands for each OS are on this page.

Is CVE-2026-91767 being exploited?

CVE-2026-91767 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-2026-91767 affect?

CVE-2026-91767 affects php. Severity is medium (CVSS 6.5). php_openssl_matches_wildcard_name() in ext/openssl/xp_ssl.c underflows the length argument passed to memchr() when a TLS server certificate presents a wildcard name whose literal characters are together longer than the hostname being verifi

How urgent is CVE-2026-91767?

Priority 28/100. On your watchlist

Software pages

OpenSSL vulnerabilities · PHP vulnerabilities

Related CVEs

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CVE-2026-92842 MEDIUM 5.9 UPGRADE The convert.base64-encode, convert.quoted-printable-encode and convert.quoted-printable-decode stream filters
CVE-2026-109618 CRITICAL 9.8 EXPLOITED UPGRADE MITIGATE PHP Memory Corruption Vulnerability
CVE-2026-109619 HIGH 8.1 EXPLOITED UPGRADE MITIGATE PHP Stale Internal Request-State Vulnerability
CVE-2026-17544 CRITICAL 9.8 UPGRADE Attacker-provided inputs to bccomp() could lead to an out-of-bounds write with stack and heap corruption in PH

References

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