* [CVE-2026-80848][IMPORTANT] xfrm: espintcp: fix UAF during close
@ 2026-09-04 19:14 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 19:14 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80848
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: xfrm: espintcp: fix UAF during close
Commit: 29121c5e6591da527e8e36ddac7120dc527f574d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29121c5e6591da527e8e36ddac7120dc527f574d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80848
Analysis date: Fri, 04 Sep 2026 15:14:00 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES
Summary:
A race in the XFRM ESPinTCP close path can free an skb while queued reinjection work still uses it as a data source, allowing a reachable ESPinTCP peer to trigger a kernel UAF that can crash the system and may warrant confidentiality review.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80848 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80848
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: IMPORTANT
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-80848 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-80848 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A use after free can occur in the xfrm ESPinTCP close path because espintcp_close can free an skb while xfrm_trans_reinject work is still able to reach espintcp_push_msgs and skb_send_sock_locked with the same skb as a data source. A remote ESPinTCP peer or an attacker able to influence the ESP over TCP connection may be able to race socket close with queued reinjection work, causing a kernel crash and possible exposure of freed skb backed data. For the CVSS the PR:N is used for the paranoid score because no local privileges on the target are required once the ESPinTCP endpoint is configured and reachable. The issue is network reachable in IPsec over TCP deployments, but practical exposure is usually limited to systems that use RFC 8229 ESPinTCP and allow the peer or network path to trigger the close and reinjection timing. Impact is at least denial of service via kernel crash and in the worst case may include confidentiality and integrity impact due to use after free behavior in the networking stack.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES REMOTE RACE LEAK UAF NETWORK SKB LINUS KPANIC NO NO checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
## 1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::
## 2. Signal breakdown
Conservative signals:
* Remote reachable / network-triggerable: +2
The affected path is ESP-in-TCP in XFRM/IPsec. A configured ESPinTCP peer or attacker able to influence that TCP/IPsec connection may trigger the close/reinject timing remotely.
* Memory corruption, weak primitive: +1
This is a race-dependent UAF on an skb. The patch prevents a stale skb from being used after espintcp_close() frees it, but the supplied context does not show attacker-controlled reclaim, object replacement, write-after-free, callback control, or arbitrary write.
* Real lifetime corruption: +1
The bug is explicitly a lifetime issue between espintcp_close() freeing emsg->skb and xfrm_trans_reinject work later reading the same skb.
* Reliable kernel crash / strong DoS: +1
UAF of skb in the networking send path is a credible kernel crash condition.
* Hard or unreliable race / special timing required: -1
The bug depends on a close-time race between socket teardown and queued reinjection work.
Conservative total: 2 + 1 + 1 + 1 - 1 = 4.
Paranoid additional signal:
* Confidentiality impact plausible: +1
The stale skb is described as being read as a data source by skb_send_sock_locked(). This is not enough to claim a strong leak primitive, but it is enough to avoid auto-closing without manual review.
Paranoid total: 5.
No LPE bonus is awarded because the patch does not show controlled reclaim, write primitive, type confusion, callback dispatch, or refcount takeover.
## 3. Reachability analysis
The likely trigger is a remote ESPinTCP peer or an attacker who can influence an established ESP over TCP connection and race socket close against queued xfrm_trans_reinject work. No local user account on the target is inherently required once the endpoint is configured and reachable, so PR:N is defensible for the paranoid network-facing interpretation.
This is not a generic Internet-wide TCP bug. Exposure is limited to systems using XFRM/IPsec ESP-in-TCP, RFC 8229 style deployment, with reachable peers or network paths that can affect connection teardown timing. Namespaces may matter if untrusted workloads can configure or operate IPsec/XFRM state, but in typical deployments XFRM setup itself is administrative. The vulnerable packet/lifetime path is still in kernel networking and should not be treated as a low-priority niche driver issue.
Call-site confidence: high. The commit message gives the relevant chain: espintcp_close() -> kfree_skb() racing with xfrm_trans_reinject -> esp_output_tcp_finish() -> espintcp_push_skb() -> espintcp_push_msgs() -> skb_send_sock_locked().
## 4. Severity interpretation
This behaves above an ordinary Moderate because it is a network-reachable lifetime bug in XFRM/IPsec involving skb UAF and asynchronous workqueue execution. Realistic demonstrated impact is mainly DoS through kernel crash. Theoretical confidentiality impact is plausible because the freed skb can be read as a data source, but the patch does not establish attacker-controlled reclaim or a stable disclosure primitive.
This should be handled as Actionable Moderate at minimum. It is a Strong Important candidate only under a paranoid review model that treats network-reachable skb UAFs as potentially hiding stronger impact until manually excluded.
## 5. One-sentence report phrase
A race in the XFRM ESPinTCP close path can free an skb while queued reinjection work still uses it as a data source, allowing a reachable ESPinTCP peer to trigger a kernel UAF that can crash the system and may warrant confidentiality review.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: this is a ZDI-reported network-reachable race UAF in the kernel networking stack, involving skb lifetime and asynchronous reinjection work. Even though the clearly supported impact is DoS, the stale skb data-source use makes auto-closing unsafe.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xfrm: espintcp: fix UAF during close
Commit: 29121c5e6591da527e8e36ddac7120dc527f574d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29121c5e6591da527e8e36ddac7120dc527f574d
Commit description:
ZDI reported and analyzed a race condition during close for espintcp
sockets:
espintcp_close() frees emsg->skb via kfree_skb() without holding
any socket lock. Concurrently, the xfrm_trans_reinject work queue
invokes esp_output_tcp_finish() -> espintcp_push_skb() ->
espintcp_push_msgs() -> skb_send_sock_locked(), which reads the
same skb as a data source.
Fix this by adding a synchronize_rcu() call after resetting sk_prot,
since esp_output_tcp_finish() runs under RCU and won't use a socket
with sk_prot == &tcp_prot. Simply taking the socket lock in
espintcp_close() could lead to leaks, if esp_output_tcp_finish()
re-adds an skb in the slot we just freed. After this, the existing
barrier() is no longer needed.
Cc: [email protected]
Fixes: e27cca9 ("xfrm: add espintcp (RFC 8229)")
Reported-by: [email protected]
Signed-off-by: Sabrina Dubroca <[email protected]>
Reviewed-by: Breno Leitao <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/xfrm/espintcp.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29121c5e6591da527e8e36ddac7120dc527f574d
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80848 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80848
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.1
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: 4
Paranoid ActionableScore: 5
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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