A flaw was found in libsoup. When the permessage-deflate WebSocket extension compresses a very large outgoing message, truncated size calculations… (CVE-2026-102560)

CVE-2026-102560 describes a heap buffer overflow in libsoup's handling of the permessage-deflate WebSocket extension. Specifically, when compressing very large outgoing messages, truncated size calculations for GByteArray growth can wrap around, causing zlib to write past the allocated buffer boundary. This results in a heap buffer overflow condition. The issue affects libsoup versions included in Red Hat Enterprise Linux 9 and related variants. Red Hat has released patched packages to fix this vulnerability along with several other related heap buffer overflow flaws in libsoup's WebSocket implementation.

The vulnerability allows an attacker to cause a heap buffer overflow during compression of large WebSocket messages, potentially leading to memory corruption. The CVSS score of 8.6 indicates high severity with impacts to confidentiality, integrity, and availability. Exploitation could result in partial information disclosure, modification of data, or denial of service. There are no known exploits in the wild at this time.

Red Hat has released security updates for libsoup in Red Hat Enterprise Linux 9 to address this vulnerability. Users should apply the official patches provided in RHSA-2026:83384. Refer to the Red Hat advisory and update instructions at https://access.redhat.com/errata/RHSA-2026:83384 and https://access.redhat.com/articles/11258. No additional mitigation actions are required beyond applying the official fixes.