CVE-2026-6104

critical

Published 2026-05-10 · Modified 2026-05-12

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CVSS v3

9.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

CVSS v4 NEW

6.3

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:L/SC:L/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:M/U:Amber

VIR risk

9.1

Description

In PHP versions 8.4.* before 8.4.21 and 8.5.* before 8.5.6, when an encoding name containing an embedded NUL byte is passed to mb_convert_encoding() or related mbstring functions, the code incorrectly assumes that when strncasecmp() returns 0 it means the strings have the same length. This can lead to out-of-bounds read of global memory, potentially causing a crash or information disclosure or crash. Affected functions include mb_convert_encoding(), mb_detect_encoding(), mb_convert_variables(), and mb_detect_order(), as well as the mbstring.detect_order and mbstring.http_output INI settings.

Predictions

Exploit likelihood

94%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

OS impact

SUSE Affected 1 release

Version	Status	Fixed in
—	Affected	—

Debian Fixed 5 releases

Version	Status	Fixed in
trixie	Fixed	`8.4.21-1~deb13u1`
sid	Fixed	`8.4.21-1`
forky	Fixed	`8.4.21-1`
bullseye	Fixed	`0`
bookworm	Fixed	`0`

Application impact

Vendor	Product	Versions	Fixed
php	php	`{"startIncluding":"8.4.0","endExcluding":"8.4.21"}`	`8.4.21`

References

CWEs

CWE-125

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.