CVE-2026-89477

In the Linux kernel, the following vulnerability has been resolved:

sctp: fix NULL deref on untransmitted RECONF completion

sctp process strreset outreq(), sctp process strreset addstrm out() and sctp process strreset resp() complete a pending stream reconfiguration request by stopping the reconf timer on the transport it was sent on:

t = asoc->strreset chunk->transport;
if (timer delete(&t->reconf timer))
	sctp transport put(t);

chunk->transport is assigned by sctp packet append chunk() when the chunk is appended to an outbound packet, and sctp outq flush ctrl() arms the reconf timer at that same point. A request already published in asoc->strreset chunk but not yet transmitted has neither, so completing it dereferences NULL.

Two ways to get there. sctp send asconf del ip() sets asoc->src out of asoc ok without sending anything when the address being removed is the association's last one, and sctp outq flush ctrl() then leaves every non-ASCONF control chunk queued; as only sctp process asconf ack() clears that flag, it persists. An unprivileged process that removes such an address and then asks for a stream reset panics the kernel from softirq. A peer needs neither ASCONF nor local help: sctp cmd interpreter() uncorks the outqueue only once the whole packet has been processed, so a reply built while walking a RECONF chunk stays untransmitted for the rest of that walk, and one RECONF chunk carrying [Incoming SSN Reset Request, Outgoing SSN Reset Request, Response] -- or two RECONF chunks in one packet -- reaches the same dereference.

KASAN: null-ptr-deref in range [0x00000000000001e8-0x00000000000001ef] RIP: 0010:timer delete+0x67/0x110 Call Trace: sctp process strreset addstrm out (net/sctp/stream.c:832) sctp sf do reconf (net/sctp/sm statefuns.c:4212) sctp do sm (net/sctp/sm sideeffect.c:1172) sctp assoc bh rcv (net/sctp/associola.c:1044) sctp rcv (net/sctp/input.c:243) ip local deliver (net/ipv4/ip input.c:262) process backlog (net/core/dev.c:6680)

A response can only acknowledge a request that was actually sent, so do not match asoc->strreset chunk while chunk->transport is NULL. Guarding the lookup covers all three completion sites.