Rhodri James discovered a heap use-after-free vulnerability in the doContent function in Expat, an XML parsing C library, which could result in denial of service or potentially the execution of arbitrary code, if a malformed XML file is processed.
For the stable distribution (bullseye), this problem has been fixed in version 2.2.10-2+deb11u4.
We recommend that you upgrade your expat packages.
For the detailed security status of expat please refer to its security tracker page at: https://security-tracker.debian.org/tracker/expat