CVE-2026-6104

CVE-2026-6104 is a critical-severity vulnerability in Php with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-125.

Key facts

• Severity: Critical (CVSS 3.x base score 9.1)
• CVSS v4: 6.3
• EPSS exploit prediction: 0% (37th percentile)
• Actively exploited: Not listed in CISA KEV
• EU (EUVD) id: EUVD-2026-28979
• Weakness: CWE-125
• Affected product: Php
• Published: 2026-05-10
• Last modified: 2026-06-30

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.

Frequently asked questions

What is CVE-2026-6104?

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.

How severe is CVE-2026-6104?

CVE-2026-6104 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability high.

Is CVE-2026-6104 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-6104?

CVE-2026-6104 affects Php. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-6104?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-6104 have an EU (EUVD) identifier?

Yes. CVE-2026-6104 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-28979.

When was CVE-2026-6104 published?

CVE-2026-6104 was published on 2026-05-10 and last updated on 2026-06-30.

References

• https://github.com/php/php-src/security/advisories/GHSA-74r9-qxhc-fx53
• https://access.redhat.com/errata/RHSA-2026:22649
• https://access.redhat.com/security/cve/CVE-2026-6104
• https://bugzilla.redhat.com/show_bug.cgi?id=2468573
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-6104.json

Affected products (1)

• cpe:2.3:a:php:php:*:*:*:*:*:*:*:*

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Other CWE-125 (Out-of-bounds Read) vulnerabilities

• CVE-2026-24826 — Critical (CVSS 10.0): Out-of-bounds Write, Divide By Zero, NULL Pointer Dereference, Use of Uninitialized Resource, Out-of-bounds Read,…
• CVE-2024-22004 — Critical (CVSS 10.0): Due to length check, an attacker with privilege access on a Linux Nonsecure operating system can trigger a…
• CVE-2021-41556 — Critical (CVSS 10.0): sqclass.cpp in Squirrel through 2.2.5 and 3.x through 3.1 allows an out-of-bounds read (in the core interpreter) that…
• CVE-2021-21777 — Critical (CVSS 10.0): An information disclosure vulnerability exists in the Ethernet/IP UDP handler functionality of EIP Stack Group OpENer…
• CVE-2017-14451 — Critical (CVSS 10.0): An exploitable out-of-bounds read vulnerability exists in libevm (Ethereum Virtual Machine) of CPP-Ethereum. A…
• CVE-2013-0767 — Critical (CVSS 10.0): The nsSVGPathElement::GetPathLengthScale function in Mozilla Firefox before 18.0, Firefox ESR 10.x before 10.0.12 and…

Browse all CWE-125 (Out-of-bounds Read) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

• 82.39.35.211 (ipv4-addr)
• 103.76.120.225 (ipv4-addr)
• 162.240.179.173 (ipv4-addr)
• 51.75.149.221 (ipv4-addr)