The vulnerability lies in the establish_proxy_connection() function of rsync, where an off‑by‑one out‑of‑bounds write occurs on the stack when parsing a proxy response line that is 1023 bytes or longer without a newline terminator. Triggering the write corrupts the stack and can cause crashes, memory corruption, or potentially code execution, depending on how the corrupted data is later used. The weakness is classified as CWE‑193, an off‑by‑one error that affects reliability and integrity of the process.

RsyncProject’s rsync software is affected. All releases prior to version 3.4.3 are vulnerable. No specific sub‑versions are listed beyond the generic "< 3.4.3" directive.

The CVSS score of 2.1 denotes a low severity impact, and the EPSS score is not available, implying no known widespread exploitation at this time. The vulnerability is not listed in CISA KEV. An attacker must position themselves on the network path between an rsync client and its HTTP proxy or control the proxy to send a long response line; the environment variable RSYNC_PROXY must be set for the exploit to trigger. Given these prerequisites, the risk remains low but remediation is advisable.