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Response snapshot Oct 26, 2026, 22:38 UTC

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VulnerabilityCVE-2026-98548

Linux kernel: sctp: discard the rest of the packet on a stale-cookie error

In the Linux kernel, the following vulnerability has been resolved: sctp: discard the rest of the packet on a stale-cookie error When an association is in COOKIE-ECHOED state and the peer sends a bundled [ERROR(Stale Cookie)][DATA] packet from one of its non-primary addresses, processing the ERROR chunk takes the non-fatal stale-cookie retry path sctp_sf_do_5_2_6_stale(), which queues SCTP_CMD_DEL_NON_PRIMARY while keeping the association alive.

Published Updated

At a glance

Exploited
Not known
Severity
9.8 Critical (CVSS 3.1)
Chance of exploitation
0.7% in the next 30 days
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-98548 (opens a new tab)

What happened

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

sctp: discard the rest of the packet on a stale-cookie error

When an association is in COOKIE-ECHOED state and the peer sends a bundled [ERROR(Stale Cookie)][DATA] packet from one of its non-primary addresses, processing the ERROR chunk takes the non-fatal stale-cookie retry path sctp_sf_do_5_2_6_stale(), which queues SCTP_CMD_DEL_NON_PRIMARY while keeping the association alive.

sctp_cmd_del_non_primary() removes every non-primary transport - including the very transport this packet arrived on, which is still referenced by the receive lookup and shared by all chunks of the packet via chunk->transport.

Continue reading

sctp_assoc_rm_peer() does redirect asoc->peer.last_data_from away from the removed transport, but right afterwards the bundled DATA chunk makes sctp_assoc_bh_rcv() re-register asoc->peer.last_data_from = chunk->transport unconditionally, undoing the redirection with the just-removed transport.

Once the packet is done, the receive reference is dropped and the transport is RCU-freed, while the surviving association keeps the dangling last_data_from. A later FWD-TSN (or the delayed SACK timer) makes sctp_gen_sack() dereference it (->param_flags and friends), and sctp_make_sack()/sctp_outq_select_transport() may write to the freed object and link it into the live transport list.

This is a use-after-free triggerable by any malicious SCTP peer (or a local unprivileged user acting as one) with no capabilities required:

BUG: KASAN: slab-use-after-free in sctp_do_sm+0x498a/0x5660 Read of size 4 at addr ffff88800e1e356c by task poc/115 Call Trace: sctp_do_sm <- sctp_assoc_bh_rcv <- sctp_inq_push <- sctp_rcv <- ip_protocol_deliver_rcu <- ip_rcv Allocated: sctp_transport_new <- sctp_assoc_add_peer <- sctp_process_init (INIT-ACK processing) Freed: kfree <- sctp_transport_destroy_rcu <- rcu_core (call_rcu queued by sctp_transport_put at end of sctp_rcv) The buggy address is located 364 bytes inside of freed 1024-byte region [ffff88800e1e3400, ffff88800e1e3800), cache kmalloc-1k

Note that commit 03a9d10ecf71 ("sctp: drop a chunk if its transport was removed") only covers the window between the receive lookup and the chunk processing (e.g. an ASCONF DEL-IP racing the socket backlog); here the transport is removed *while* the packet is being processed, by an earlier chunk of the same packet, so the drop in sctp_inq_push() does not reach this path.

Verified with the bundled [ERROR(Stale Cookie)][DATA] + FWD-TSN reproducer: the KASAN report above still fires with that commit applied, and is gone with this patch on top.

Fix it by discarding the rest of the packet on this path, as suggested by Xin.

After the stale-cookie ERROR has sent the association back to COOKIE-WAIT and removed the non-primary transports, the remaining chunks of the packet can only run against the restarted handshake while referencing the removed arrival transport through chunk->transport: besides the last_data_from registration above, sctp_cmd_setup_t2() and the sctp_make_*() reply builders would also copy that pointer into association-lifetime state that sctp_assoc_rm_peer() has already sanitized.

Let the peer retransmit them, in line with what sctp_inq_push() does for chunks whose transport was removed before processing.

Scores and how they were measured

CVSS base severity

9.8

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.7%

Scored Percentile 52.7%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-98548 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-98548, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 24). Linux kernel: sctp: discard the rest of the packet on a stale-cookie error (CVE-2026-98548). https://kevwire.com/record/CVE-2026-98548

MLA

"Linux kernel: sctp: discard the rest of the packet on a stale-cookie error (CVE-2026-98548)." KEVWire, 24 Oct. 2026, kevwire.com/record/CVE-2026-98548.

Chicago

KEVWire. "Linux kernel: sctp: discard the rest of the packet on a stale-cookie error (CVE-2026-98548)." Last modified October 24, 2026. https://kevwire.com/record/CVE-2026-98548.

Evidence summary (plain text)

Linux kernel: sctp: discard the rest of the packet on a stale-cookie error (Oct 18, 2026).
In the Linux kernel, the following vulnerability has been resolved:

sctp: discard the rest of the packet on a stale-cookie error

When an association is in COOKIE-ECHOED state and the peer sends a
bundled [ERROR(Stale Cookie)][DATA] packet from one of its non-primary
addresses, processing the ERROR chunk takes the non-fatal stale-cookie
retry path sctp_sf_do_5_2_6_stale(), which queues
SCTP_CMD_DEL_NON_PRIMARY while keeping the association alive.
sctp_cmd_del_non_primary() removes every non-primary transport -
including the very transport this packet arrived on, which is still
referenced by the receive lookup and shared by all chunks of the
packet via chunk->transport.

sctp_assoc_rm_peer() does redirect asoc->peer.last_data_from away from
the removed transport, but right afterwards the bundled DATA chunk
makes sctp_assoc_bh_rcv() re-register
asoc->peer.last_data_from = chunk->transport unconditionally, undoing
the redirection with the just-removed transport.

Once the packet is done, the receive reference is dropped and the
transport is RCU-freed, while the surviving association keeps the
dangling last_data_from.  A later FWD-TSN (or the delayed SACK timer)
makes sctp_gen_sack() dereference it (->param_flags and friends), and
sctp_make_sack()/sctp_outq_select_transport() may write to the freed
object and link it into the live transport list.  This is a
use-after-free triggerable by any malicious SCTP peer (or a local
unprivileged user acting as one) with no capabilities required:

  BUG: KASAN: slab-use-after-free in sctp_do_sm+0x498a/0x5660
  Read of size 4 at addr ffff88800e1e356c by task poc/115
  Call Trace: sctp_do_sm <- sctp_assoc_bh_rcv <- sctp_inq_push <-
              sctp_rcv <- ip_protocol_deliver_rcu <- ip_rcv
  Allocated: sctp_transport_new <- sctp_assoc_add_peer <-
             sctp_process_init (INIT-ACK processing)
  Freed: kfree <- sctp_transport_destroy_rcu <- rcu_core
         (call_rcu queued by sctp_transport_put at end of sctp_rcv)
  The buggy address is located 364 bytes inside of freed 1024-byte
  region [ffff88800e1e3400, ffff88800e1e3800), cache kmalloc-1k

Note that commit 03a9d10ecf71 ("sctp: drop a chunk if its transport
was remove
CVSS 9.8 (version 3.1; evidence as of Oct 24, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-98548).
EPSS 0.7% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-98548&date=2026-10-26).
Sources:
NVD CVE-2026-98548: https://nvd.nist.gov/vuln/detail/CVE-2026-98548
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=4500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-98548&date=2026-10-26
Record ID: CVE-2026-98548.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

NVD status: Received. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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