Bug 2521434 (CVE-2026-74587)

Summary: CVE-2026-74587 kernel: sctp: fix use-after-free of cached ASCONF chunk
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Stream Control Transmission Protocol (SCTP) implementation. During peer restart handling, the system improperly releases a cached ASCONF chunk without clearing its pointer, leading to a use-after-free vulnerability. A remote attacker could exploit this by sending a delayed authenticated ASCONF-ACK, causing the system to access freed memory. This could result in a system crash, leading to a denial of service.
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Description OSIDB Bzimport 2026-08-22 15:45:25 UTC 
In the Linux kernel, the following vulnerability has been resolved:

sctp: fix use-after-free of cached ASCONF chunk

addip_last_asconf caches the outstanding outbound ASCONF chunk. The normal
ASCONF-ACK completion path releases the chunk and clears the pointer.

However, sctp_asconf_queue_teardown() releases the cached chunk without
clearing addip_last_asconf. During peer restart handling,
sctp_sf_do_dupcook_a() queues SCTP_CMD_PURGE_ASCONF_QUEUE, which invokes
sctp_asconf_queue_teardown() while the association remains alive and leaves
the pointer dangling.

A delayed authenticated ASCONF-ACK can then reach sctp_sf_do_asconf_ack(),
which accesses the stale chunk and passes it to sctp_process_asconf_ack(),
causing a use-after-free and a second release.

Clearing the pointer exposes a race with T4 expiry. Peer restart handling
queues the timer stop before the purge, but SCTP_CMD_TIMER_STOP uses
timer_delete(), which does not wait for a callback already running on
another CPU. Such a callback can reach sctp_sf_t4_timer_expire() after
the purge and dereference NULL.

Clear addip_last_asconf after releasing the cached chunk, and make
sctp_sf_t4_timer_expire() consume a stale T4 expiry if no outstanding
ASCONF remains.
Comment 1 Keith Grant 2026-08-24 12:32:48 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082212-CVE-2026-74587-d6f8@gregkh/T