CVE-2026-2903 identifies a null pointer dereference vulnerability in the open-source tool skvadrik re2c, specifically affecting versions 4.0 through 4.4. The flaw resides in the function check_and_merge_special_rules located in src/parse/ast.cc, where improper handling of certain inputs leads to dereferencing a null pointer. This results in a crash of the re2c process, causing a denial of service. The vulnerability requires local access with low privileges, meaning an attacker must have some level of access to the host system to exploit it. No authentication or user interaction is necessary beyond local presence. The vulnerability does not affect confidentiality or integrity, as it only causes a process crash without code execution or data leakage. The exploit has been publicly disclosed, increasing the risk of local denial of service attacks. A patch identified by commit febeb977936f9519a25d9fbd10ff8256358cdb97 has been released to fix the issue. The CVSS v4.0 base score is 4.8, reflecting a medium severity level due to the limited attack vector (local), low complexity, and no privilege escalation or network exploitation. The vulnerability is relevant primarily to developers and organizations using re2c for lexer generation in software projects.

The primary impact of CVE-2026-2903 is a denial of service condition caused by a null pointer dereference crash in re2c. This can disrupt development workflows or automated build systems relying on re2c, potentially delaying software releases or automated testing. Since exploitation requires local access, the threat is mostly relevant in multi-user environments, shared development servers, or compromised systems where an attacker has gained limited access. There is no direct risk to data confidentiality or integrity, nor is there evidence of privilege escalation or remote exploitation. However, denial of service in critical build or CI/CD environments could indirectly impact organizational productivity and operational continuity. The public availability of an exploit increases the likelihood of opportunistic attacks in environments where re2c is used without patching. Overall, the impact is moderate and mostly operational rather than security-critical.

To mitigate CVE-2026-2903, organizations should promptly apply the official patch identified by commit febeb977936f9519a25d9fbd10ff8256358cdb97 to all affected re2c installations (versions 4.0 through 4.4). In addition, restrict local access to systems running re2c to trusted users only, minimizing the risk of local exploitation. Implement strict user privilege separation and monitor local user activities for suspicious behavior. For build servers and CI/CD pipelines using re2c, consider isolating build environments and employing containerization to limit the impact of potential crashes. Regularly update development tools and dependencies to incorporate security fixes. Finally, maintain an inventory of software development tools to quickly identify and remediate vulnerable versions.