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CVE-2026-6104— Global buffer over-read in mb_convert_encoding() with attacker-supplied encoding

Quick assessment

Affected
PHP Group PHP
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

PHP是PHP开源的一种在服务器端执行的脚本语言。 PHP 8.4.21之前版本和8.5.6之前版本存在缓冲区错误漏洞，该漏洞源于当包含嵌入NUL字节的编码名称传递给mb_convert_encoding()或相关mbstring函数时，代码错误地假设strncasecmp()返回0意味着字符串长度相同，可能导致全局内存越界读取，从而引发崩溃或信息泄露。以下版本受到影响：8.4.21之前版本和8.5.6之前版本。

AI Predicted 7.5 Difficulty: Easy EPSS 0.60% · P47

Possible ATT&CK Techniques 1 AI

T1005 · Data from Local System

Affected Version Matrix 2

VendorProduct Version RangeStatus
PHP Group PHP 8.4.*< 8.4.21 affected
8.5.*< 8.5.6 affected
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I. Basic Information for CVE-2026-6104

Vulnerability Information
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Vulnerability Title
Global buffer over-read in mb_convert_encoding() with attacker-supplied encoding
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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/RE:M/U:Amber
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5
Vulnerability Title
PHP 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
PHP是PHP开源的一种在服务器端执行的脚本语言。 PHP 8.4.21之前版本和8.5.6之前版本存在缓冲区错误漏洞，该漏洞源于当包含嵌入NUL字节的编码名称传递给mb_convert_encoding()或相关mbstring函数时，代码错误地假设strncasecmp()返回0意味着字符串长度相同，可能导致全局内存越界读取，从而引发崩溃或信息泄露。以下版本受到影响：8.4.21之前版本和8.5.6之前版本。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
PHP Group PHP 8.4.* ~ 8.4.21 -

II. Public POCs for CVE-2026-6104

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III. Intelligence Information for CVE-2026-6104

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Vendor Advisories for CVE-2026-6104 (1)

Same Patch Batch · PHP Group · 2026-05-10 · 10 CVEs total

CVE-2026-6722 9.5 CRITICAL Use-After-Free in SOAP using Apache map
CVE-2026-7258 Out-of-bounds read in urldecode() on NetBSD
CVE-2026-7262 NULL pointer dereference in SOAP apache:Map decoder with missing <value>
CVE-2026-7261 SoapServer session-persisted object use-after-free via SOAP header fault
CVE-2026-7259 Null pointer dereference in php_mb_check_encoding() via mb_ereg_search_init()
CVE-2026-7568 Signed integer overflow in metaphone()
CVE-2026-6735 XSS within PHP-FPM status endpoint
CVE-2025-14179 SQL injection in pdo_firebird via NUL bytes in quoted strings
CVE-2026-7263 DoS attack via DOMNode::C14N()

IV. Related Vulnerabilities

Same product: PHP
Same vendor: PHP Group
Same weakness: CWE-125

V. Comments for CVE-2026-6104

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