OpenResty versions from 1.29.2.1 through 1.29.2.4 contain an out‑of‑bounds write in the code that builds PROXY protocol headers for outgoing connections to upstream servers. When the header is constructed, the buffer is written beyond its allocated limits, causing a worker process to crash and leading to a temporary denial of service for the affected upstream session. The flaw is a classic example of CWE‑787 out‑of‑bounds write.

The vulnerability affects OpenResty deployments that are configured to send PROXY protocol version 2 headers to upstream servers. Any installation running OpenResty between versions 1.29.2.1 and 1.29.2.4, inclusive, is impacted. Versions 1.29.2.5 and later contain a fix that removes the overflow.

The CVSS score of 7.5 indicates a serious impact, and the EPSS score of less than 1 % suggests a very low probability of exploitation at present. The vulnerability is not listed in CISA KEV. Based on the description it is inferred that an attacker would need the ability to direct requests to an upstream endpoint that has PROXY protocol v2 enabled, and that the attack would trigger a worker crash leading to denial of service. No additional privileges are required beyond being able to send traffic to the vulnerable server.