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🛡️ CVE-2026-6104 on Ubuntu — php8.4

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

Distribution advisory

This page covers CVE-2026-6104 as tracked by Ubuntu, for the package php8.4. The fix is available in version 8.4.11-1ubuntu1.2; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Affected software

UBUNTU-CVE-2026-6104 is recorded against 2 packages.

  • php8.4 (fixed in 8.4.11-1ubuntu1.2)
  • php8.5 (fixed in 8.5.4-0ubuntu1.1)

Timeline and source

Published on 10 May 2026 and last revised on 30 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

ubuntu.com (Report)
www.cve.org (Report)
github.com (Report)
ubuntu.com (Advisory)

Other advisories for this package

php8.4 has other advisories on record. If you are patching this one, these are worth checking on the same host:

CVE-2026-6104 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-05-10
Updated 2026-08-20
Modified 2026-06-30
Fix URL N/A

Affected Packages

Software From version Fixed in
php8.4 — 8.4.11-1ubuntu1.2
php8.5 — 8.5.4-0ubuntu1.1

Vulnerability Monitoring

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