Corosync is a group communication system providing reliable ordered messaging and membership services, and is the communication layer underlying Pacemaker HA clusters (RHEL High Availability Add-On). In exec/totempg.c, the totempg_deliver_fn function reassembles fragmented multicast messages into a fixed-size per-node assembly buffer (struct assembly, data[MESSAGE_SIZE_MAX + KNET_MAX_PACKET_SIZE], ~1.06 MB on normal builds, ~128 KB on small-memory-footprint builds). The only bounds check before the memcpy at line 663 is an assert() at line 662, which is compiled out in release builds (-DNDEBUG). assembly->index grows unboundedly at line 737 for each continuation fragment with no upper-bound check. After 17-18 fragments on normal builds (3 fragments on small-memory-footprint builds), the memcpy writes attacker-controlled data past the end of the heap buffer.

Verified via an ASan-instrumented standalone harness reproducing the exact buffer layout and memcpy/index logic: after 17 fragments of 65,481 bytes each, assembly->index reached 1,113,177 (buffer capacity 1,114,112); fragment 18 triggered a confirmed heap-buffer-overflow WRITE of 65,481 bytes, 64,546 bytes past the buffer end.

Present in corosync v3.1.10 (latest upstream release) and main HEAD (commit 65235a8); no upstream fix exists for this bug. Reported by Tristan Madani (Talence Security) via PSIRTSUPT-22352.