CVE-2026-2903 in re2c
Summary
by MITRE • 02/22/2026
A flaw has been found in skvadrik re2c up to 4.4. Impacted is the function check_and_merge_special_rules of the file src/parse/ast.cc. This manipulation causes null pointer dereference. The attack can only be executed locally. The exploit has been published and may be used. Patch name: febeb977936f9519a25d9fbd10ff8256358cdb97. It is suggested to install a patch to address this issue.
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability identified as CVE-2026-2903 represents a critical null pointer dereference flaw within the skvadrik re2c tool version 4.4 and earlier. This security issue resides in the check_and_merge_special_rules function located within the src/parse/ast.cc source file, demonstrating a fundamental programming error that can lead to system instability and potential exploitation. The re2c tool serves as a regular expression compiler that generates C code from regular expression patterns, making it a crucial component in various software development workflows and automated build processes.
The technical nature of this vulnerability stems from improper null pointer validation within the function responsible for processing and merging special rules during the parsing phase of regular expression compilation. When the function encounters certain input patterns or edge cases, it fails to properly validate pointer references before dereferencing them, creating a scenario where a null pointer is accessed and causes the application to crash or behave unpredictably. This type of flaw falls under CWE-476 which specifically addresses null pointer dereference conditions that can result in denial of service or potentially more severe consequences depending on the execution context.
Operationally, this vulnerability presents a local privilege escalation risk as the attack vector requires local system access to execute successfully. The fact that a working exploit has been published increases the threat level significantly, as it removes the barrier to entry for malicious actors who wish to leverage this weakness. The impact extends beyond simple system crashes, as the null pointer dereference can potentially be chained with other vulnerabilities or used to create more sophisticated attack vectors within the local environment. Attackers could utilize this flaw to cause service disruption, potentially leading to denial of service conditions that affect legitimate users of the affected systems.
The recommended mitigation strategy involves applying the patch identified by the commit hash febeb977936f9519a25d9fbd10ff8256358cdb97, which contains the necessary code modifications to properly validate pointer references before dereferencing. System administrators should prioritize patching affected installations, particularly in development environments where re2c is actively used for regular expression compilation. Organizations should also implement monitoring for unusual process termination patterns or system crashes that might indicate exploitation attempts. Additionally, implementing proper input validation and sanitization practices in applications that utilize re2c could provide additional defense-in-depth measures against similar vulnerabilities. The ATT&CK framework categorizes this type of vulnerability under T1499 which covers endpoint detection and response considerations for denial of service attacks, making it important for security teams to monitor for such patterns in their environments.