CVE-2026-108741: Time-of-check Time-of-use (TOCTOU) Race Condition in shepherd-agents Shepherd

CVE-2026-108741 describes a TOCTOU race condition in Shepherd (shepherd-ai) through version 0.3.1. The issue arises because the public_url guard validates a resolved address, but the fetch operation re-resolves the hostname at connect time. An attacker who plants a crafted reference URL in a document checked by the citation-checker and controls its DNS can rebind the hostname to internal addresses after validation. This allows sending GET requests to internal HTTP(S) services and capturing their responses in evidence files, effectively bypassing the SSRF guard.

The vulnerability enables attackers to bypass the SSRF protection in Shepherd's citation-checker, potentially allowing unauthorized internal HTTP(S) requests and exfiltration of internal service responses. However, the impact is limited by the low CVSS score (2.3), indicating low severity and requiring user interaction. There are no known exploits in the wild.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should be cautious about processing documents containing untrusted reference URLs and consider restricting DNS control or network access to internal services to mitigate potential exploitation.