A remote attacker can cause a denial of service by sending a POST request to the /rerank endpoint of the llama.cpp library when the program has been started with the --reranking flag. The attacker exploits a flaw in which a negative top_n value is not validated before being passed to C++ code. This causes a std::bad_alloc exception, resulting in the server returning an HTTP 500 error and temporarily halting the service. The weakness is an input validation flaw that lets malformed data crash the process.

The open‑source llama.cpp project contains the vulnerability in any build that has the reranking feature enabled prior to commit 97f06e9. Developers and operators who build or deploy those versions and expose the /rerank endpoint are impacted. No vendor or product information is supplied for this CVE.

With a CVSS score of 7.5 and an EPSS score of less than 1 %, the attack surface is relatively low, yet the denial‑of‑service outcome can be achieved with a single, unauthenticated POST request. The endpoint is reachable over HTTP and likely does not require authentication, making the risk broader for exposed deployments. Although the vulnerability is not yet listed in CISA’s KEV catalog, the remote nature and potential to disrupt service warrant timely mitigation.