CVE-2026-89160 in PCRE2
Summary
by MITRE • 09/11/2026
PCRE2 before 10.48 has a pcre2_match out-of-bounds read during the PCRE2_MATCH_INVALID_UTF matching of an invalid UTF subject.
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Analysis
by VulDB Data Team • 09/11/2026
The Perl Compatible Regular Expressions version two library, commonly known as PCRE2, is a widely adopted open-source software library used for processing regular expressions in numerous programming languages and applications including PHP, Python, Apache HTTP Server, and various network security appliances. A critical vulnerability exists within the pcre2_match function when it processes input strings that are intended to be valid UTF-8 encoded text but contain malformed sequences. Specifically, under the PCRE2_MATCH_INVALID_UTF matching mode, which is designed to allow pattern matching on invalid UTF-8 data by treating each byte as a separate character rather than rejecting the string outright, an out-of-bounds read occurs during the execution of certain complex patterns. This flaw stems from incorrect boundary checks within the regex engine's internal state machine when handling specific edge cases involving multi-byte sequences that fail validation but are still processed due to the permissive matching mode enabled by the flag.
From a technical perspective, this vulnerability is classified as CWE-125 Out-of-bounds Read, which allows an attacker to read memory contents beyond the intended buffer boundaries. The root cause lies in the logic that calculates offsets and lengths when iterating through invalid UTF-8 sequences. When the engine encounters a byte sequence that does not conform to valid UTF-8 standards but is permitted by the PCRE2_MATCH_INVALID_UTF flag, it attempts to map these bytes into character classes or perform quantifier operations. Due to an off-by-one error in the pointer arithmetic used to track the current position within the subject string relative to the compiled pattern's internal structures, the engine may access memory locations that are not part of the allocated input buffer. This can lead to the leakage of sensitive information from adjacent memory regions if the read data is subsequently returned or processed by the calling application.
The operational impact of this vulnerability depends heavily on how PCRE2 is integrated into the host application and whether the return value of pcre2_match is utilized in a way that exposes the out-of-bounds data to the user or network. In web server contexts, such as Apache with mod_php, an attacker could potentially craft malicious HTTP requests containing specially crafted regular expressions combined with invalid UTF-8 payloads to trigger this condition. If the application logs match results or returns partial matches derived from these reads, it may result in a remote information disclosure vulnerability. Furthermore, while primarily classified as a read-only issue, out-of-bounds reads can sometimes be leveraged in conjunction with other vulnerabilities to achieve arbitrary code execution by leaking pointers that bypass address space layout randomization protections. This aligns with the ATT&CK technique T1083 File and Directory Discovery or more broadly information exfiltration techniques where memory contents are harvested for further exploitation steps.
Mitigation strategies primarily involve upgrading PCRE2 to version 10.48 or later, which contains patches that correct the boundary checking logic within the UTF-8 validation routines under invalid matching modes. For applications unable to upgrade immediately due to dependency constraints, developers should consider disabling the PCRE2_MATCH_INVALID_UTF flag if strict UTF-8 compliance is acceptable for their use case, thereby forcing the engine to reject malformed input rather than attempting to process it in a permissive manner. Additionally, implementing robust input validation at the application layer before passing data to regex engines can reduce the attack surface by filtering out potentially malicious payloads that exploit edge cases in encoding handling. Security teams should also monitor for unusual memory access patterns or segmentation faults associated with high-volume regular expression processing as indicators of potential exploitation attempts against unpatched systems.