Global buffer over-read in mb_convert_encoding() with attacker-supplied encoding

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

• CVE-2026-6104: 0.47% estimated exploitation activity in the next 30 days; percentile 41.05 (FIRST EPSS, 2026-11-12). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

12 May 2026, 08:50 UTC

Last modified by the source

11 Nov 2026, 02:55 UTC

Source last checked

11 Nov 2026, 07:55 UTC

1. Revision 3 · amended · 11 Nov 2026

   Amended from osv record BIT-php-min-2026-6104

2. Revision 2 · amended · 11 Nov 2026

   Amended from osv record BIT-php-2026-6104

3. Revision 1 · created · 11 Nov 2026

   Published from osv record BIT-libphp-2026-6104

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# Patch Next advisory brief: CVE-2026-6104

Advisory: Global buffer over-read in mb_convert_encoding() with attacker-supplied encoding
IDs: CVE-2026-6104, GHSA-74r9-qxhc-fx53
Record: https://patchnext.com/advisories/cve-2026-6104 (revision 3, source checked 11 Nov 2026, 07:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: php 8.5.6, 8.4.21; libphp 8.5.6, 8.4.21; php-min 8.5.6, 8.4.21. A vendor fix does not mean a deployment is fixed.

## Affected components
- Bitnami php: affected >= 8.4.0, < 8.4.21; >= 8.5.0, < 8.5.6; fixed in 8.5.6, 8.4.21
- Bitnami libphp: affected >= 8.4.0, < 8.4.21; >= 8.5.0, < 8.5.6; fixed in 8.5.6, 8.4.21
- Bitnami php-min: affected >= 8.4.0, < 8.4.21; >= 8.5.0, < 8.5.6; fixed in 8.5.6, 8.4.21

## Suggested inspection (read-only)
- Bitnami php: check the installed version with your package manager.
- Bitnami libphp: check the installed version with your package manager.
- Bitnami php-min: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on php, libphp, php-min.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/BIT-php-2026-6104 (OSV record BIT-php-2026-6104 lists affected ranges: Bitnami php >=8.4.0 =8.5.0 <8.5.6 (fixed))
- Verified: https://osv.dev/vulnerability/BIT-libphp-2026-6104 (OSV record BIT-libphp-2026-6104 lists affected ranges: Bitnami libphp >=8.4.0 =8.5.0 <8.5.6 (fixed))
- Verified: https://osv.dev/vulnerability/BIT-php-min-2026-6104 (OSV record BIT-php-min-2026-6104 lists affected ranges: Bitnami php-min >=8.4.0 =8.5.0 <8.5.6 (fixed))

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