libexpat versions prior to 2.8.2 contain an integer overflow in the copyString routine. The overflow can corrupt adjacent memory, potentially enabling arbitrary code execution or causing a crash if the affected application runs with elevated privileges.

The vulnerability affects the libexpat project’s libexpat library in all releases before 2.8.2. Any system or application that links against this older library is at risk.

The CVSS score of 6.9 indicates moderate severity. No EPSS data is available, and the issue is not listed in the CISA KEV catalog. Attackers would need to supply a specially crafted input that triggers the overflow, so the attack vector is inferred as local or potentially remote if the library processes untrusted input from network or otherwise. The vulnerability can be exploited by an attacker who can influence the input to copyString.