CVE-2026-42075: 
JavaScript vulnerability analysis and mitigation

CVE-2026-42075 is a path traversal vulnerability (CWE-22) in Evolver, a GEP-powered self-evolving engine for AI agents published as the npm package @evomap/evolver. The flaw exists in the skill download (fetch) command, where the --out= flag accepts user-provided filesystem paths without any validation, enabling attackers to write files to arbitrary locations on the host. All versions prior to 1.69.3 are affected. The vulnerability was disclosed on April 20, 2026 via a GitHub Security Advisory and assigned CVE-2026-42075 on May 4, 2026. It carries a CVSS v3.1 base score of 8.1 (High) (GitHub Advisory).

The root cause is improper input validation (CWE-22) in index.js at lines 752–767, where the --out= flag value is extracted via outFlag.slice('--out='.length) and used directly as the output directory without sanitization or path canonicalization. While the safeId variable (used for the default path) is sanitized with a character-allowlist regex, this sanitization is never applied to the user-supplied --out= path. An attacker with low-privilege access to the application can supply traversal sequences such as ../../../etc/cron.d to redirect file writes outside the intended skills/ directory. A proof-of-concept demonstrating the traversal is included in the advisory itself (GitHub Advisory).

Successful exploitation allows a low-privileged attacker to write arbitrary files anywhere on the filesystem that the Evolver process has write access to. This can result in overwriting critical system files, planting persistent backdoors in cron directories (/etc/cron.d), modifying SSH authorized_keys files, or overwriting application code and configuration. If Evolver runs with elevated privileges (e.g., in CI/CD pipelines or automated agent environments), the impact extends to full privilege escalation and system compromise. There is no confidentiality impact, but integrity and availability are rated High (GitHub Advisory).

No public exploit kit or weaponized exploit has been observed in the wild as of the time of disclosure. The GitHub Security Advisory includes a functional proof-of-concept script demonstrating the traversal, lowering the barrier for exploitation. The EPSS score is approximately 0.0023 (low probability of near-term exploitation). There is no current CISA KEV catalog listing for this CVE. Exploitation requires low privileges (authenticated access to the Evolver application) and no user interaction (GitHub Advisory, Feedly).

1. Identify target: Locate an environment running @evomap/evolver prior to version 1.69.3, particularly in automated or CI/CD contexts where the process may run with elevated privileges.
2. Obtain low-privilege access: Gain access to the system or application interface sufficient to invoke the Evolver CLI (e.g., a developer account, CI runner, or agent environment).
3. Craft malicious fetch command: Invoke the fetch command with a path traversal payload in the --out= flag, e.g.:

   node index.js fetch <skill-id> --out=../../../etc/cron.d

4. Trigger file write: Evolver downloads the skill files and writes them to the attacker-controlled directory (e.g., /etc/cron.d/), bypassing the intended skills/ output directory.
5. Achieve persistence or escalation: The written file (e.g., a cron job script or SSH authorized_keys entry) executes under the target user's or root's context, enabling persistent backdoor access or privilege escalation (GitHub Advisory).

• File System: Unexpected files created in sensitive directories such as /etc/cron.d/, /etc/cron.hourly/, ~/.ssh/authorized_keys, or application config directories; presence of skill.js or other Evolver skill artifacts outside the expected ./skills/ directory.
• Logs: Node.js process logs or application logs showing fetch command invocations with --out= flags containing ../ sequences; fs.mkdirSync or fs.writeFileSync calls resolving to paths outside the project root.
• Process: Unexpected cron job execution or new SSH login events following Evolver fetch command activity; child processes spawned from cron jobs or SSH sessions not attributable to normal user activity.
• Network: Outbound connections from the server to attacker-controlled infrastructure shortly after a fetch command is executed, potentially indicating a reverse shell or beacon established via a written cron job (GitHub Advisory).

The vulnerability is patched in Evolver version 1.69.3; all users should upgrade the @evomap/evolver npm package immediately (GitHub Release). As interim workarounds: restrict use of the --out= flag in automated or untrusted environments; enforce filesystem-level write restrictions (e.g., via OS permissions or containers) so the Evolver process can only write to its intended working directory; and implement input validation on the --out= flag to reject paths containing ../ or absolute path components. Running Evolver with the least-privilege principle (non-root, restricted service account) limits the blast radius of exploitation (GitHub Advisory).

The vulnerability was reported by security researcher xeloxa and disclosed by maintainer autogame-17 via GitHub's coordinated disclosure process. A brief mention appeared on Mastodon via @thehackerwire, indicating minor community awareness. No significant vendor statements beyond the advisory or major media coverage have been identified at this time (GitHub Advisory).