CVE-2026-89157 in PCRE2
Summary
by MITRE • 09/11/2026
PCRE2 before 10.48, on 32-bit platforms, has a pcre2_pattern_convert out-of-bounds write when an attacker can provide a large pattern.
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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 parsing and matching regular expressions in various programming languages and applications including PHP, Python, and Apache HTTP Server. A critical security flaw exists within the pcre2_pattern_convert function when operating on 32-bit architectures with versions prior to 10.48. This vulnerability manifests as an out-of-bounds write condition triggered by a specifically crafted regular expression pattern of significant size provided by an attacker. The root cause lies in improper boundary checks during the internal processing and conversion logic, where the library fails to correctly validate memory allocation limits relative to the input data length on 32-bit systems.
From a technical perspective, this flaw represents a classic buffer overflow scenario classified under CWE-787: Out-of-bounds Write. When an attacker supplies a large pattern string, the internal mechanisms responsible for converting or compiling the regex may miscalculate memory offsets due to integer handling limitations specific to 32-bit environments. This miscalculation allows data to be written beyond the allocated buffer boundaries into adjacent memory regions. Such unauthorized memory writes can corrupt critical application state variables, overwrite return addresses on the stack, or alter function pointers within heap structures depending on where the overflow occurs in memory layout.
The operational impact of this vulnerability is severe and potentially catastrophic for affected systems. An attacker who can control the input to a vulnerable PCRE2 implementation may achieve arbitrary code execution by exploiting the memory corruption to redirect program flow. Beyond remote code execution, this flaw also poses significant risks related to denial of service if the overflow causes immediate application crashes or segmentation faults. In web server contexts where regular expressions are processed from user-supplied HTTP headers or body content, this vulnerability can be exploited remotely without authentication, making it a high-priority target for automated exploitation campaigns targeting internet-facing services that rely on PCRE2 for request validation or routing logic.
Mitigation strategies primarily involve upgrading the PCRE2 library to version 10.48 or later where these boundary checks have been corrected and validated against large inputs. For organizations unable to immediately patch their dependencies, implementing strict input length limits on regular expression patterns served by web applications can serve as a temporary defensive measure. Additionally, deploying Web Application Firewalls with rulesets capable of detecting anomalous regex lengths may provide an additional layer of defense. Security teams should also ensure that compiler protections such as stack canaries and Address Space Layout Randomization are enabled to mitigate the exploitability of memory corruption vulnerabilities even if patching is delayed.
This vulnerability aligns with MITRE ATT&CK technique T1203: Exploitation for Client Execution, particularly in scenarios where client-side applications or servers process untrusted regex inputs that lead to code execution. It also relates to CWE-789 which covers memory corruption issues generally found in C and C++ based libraries. Continuous monitoring of dependency updates and regular vulnerability scanning against known CVEs like this one are essential components of a robust security posture for any infrastructure relying on PCRE2 for text processing tasks.