Is CVE-2026-6104 actively exploited?

No active exploitation of CVE-2026-6104 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-6104 be exploited remotely?

Yes. CVE-2026-6104 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-6104?

CVE-2026-6104 has a CVSS score of 9.1 (CRITICAL).

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CRITICAL

CVE-2026-6104

CWE-125Published: May 10, 2026· Updated: May 12, 2026

9.1

CVSS v3.1

EPSS:0.01%probability of exploitation in 30 daysPercentile:2.5th

Official 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.

NVD Source

Technical Analysis

CVE-2026-6104 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), availability disruption (denial of service), with a CVSS base score of 9.1.