[CVE-2026-80603][MODERATE 7.0] netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-80603
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read
Commit: abb8c32b88ea3f46beb68c34fe9a3ac8ed664e7e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=abb8c32b88ea3f46beb68c34fe9a3ac8ed664e7e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80603
Analysis date: Fri, 28 Aug 2026 05:04:22 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80603 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80603

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: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80603	MODERATE	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:L/I:L/A:N';CWE-193;CWE-125;CWE-908;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.8';DESCR 'An off by one read in nf_conntrack_irc parse_dcc happens because data_end is passed as one past the last valid byte but the parser treated it as an inclusive end pointer. If an IRC DCC payload has no newline inside the copied region, the loop can read one byte past the skb_header_pointer() data and simple_strtoul may consume a stale or uninitialized digit. This can produce a wrong DCC IP or port in the conntrack expectation and may weaken filtering behavior when the IRC helper is enabled for inspected traffic. For the CVSS the PR:N because a remote sender does not need an account on the target when the helper is enabled and the crafted IRC traffic is inspected by the firewall or gateway. The issue is network reachable only in deployments that enable or assign nf_conntrack_irc to IRC traffic. Impact is mainly low integrity impact through incorrect expectation creation, with possible low confidentiality impact in the paranoid interpretation. There is no clear evidence of kernel memory corruption, arbitrary write, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-80603 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE OOB SIMPLEFIX NETFILTER LINUS KPANIC PACKET  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

2. Signal breakdown
* Remote reachable / network-triggerable: +2. A crafted IRC DCC payload can reach the parser through nf_conntrack_irc when the helper is enabled or assigned to inspected traffic.
* Integrity impact plausible: +1. The stale or uninitialized byte can be consumed by simple_strtoul and may create an incorrect DCC IP or port expectation.
* Common networking core path or packet-processing path: +1. The bug is in a netfilter conntrack helper packet parsing path, although exposure depends on helper configuration.
* Confidentiality impact plausible, paranoid only: +1. The bug is a one-byte OOB read of stale or uninitialized memory, but there is no direct disclosure primitive.
* No generic memory corruption bonus. This is a limited read-only off-by-one access, not an OOB write, UAF, double free, or object lifetime corruption.
* No reliable kernel crash / strong DoS bonus. The commit states the extra allocation byte prevents a fault in the current implementation.

3. Reachability analysis
A remote sender can trigger the condition only if the target firewall or gateway inspects IRC traffic with nf_conntrack_irc. Modern deployments often do not auto-assign conntrack helpers by default, so exposure is configuration-dependent. No local account is required for the network sender once the helper is active. Namespaces do not materially lower the requirement for the remote traffic path, but local configuration of helpers normally requires administrative privileges. The realistic impact is incorrect conntrack expectation creation rather than kernel crash or privilege escalation.

4. Severity interpretation
This behaves like an actionable Moderate networking parser issue, not an Important-class memory corruption bug. Theoretical concern comes from a real off-by-one OOB read and stale-byte consumption in a packet parser. Realistic evidence supports low integrity impact through wrong expectation state, with only weak paranoid confidentiality concern and no demonstrated arbitrary read, write, crash, or LPE primitive.

5. One-sentence report phrase
An off-by-one OOB read in nf_conntrack_irc parse_dcc() can let a remote IRC payload influence DCC expectation parsing when the IRC conntrack helper is enabled, causing low integrity impact and requiring manual review despite no demonstrated crash or privilege escalation.

6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: network-reachable parser OOB read in netfilter helper code, with plausible firewall expectation manipulation even though the primitive is constrained and configuration-dependent.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: netfilter: nf_conntrack_irc: fix parse_dcc() off-by-one OOB read
Commit: abb8c32b88ea3f46beb68c34fe9a3ac8ed664e7e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=abb8c32b88ea3f46beb68c34fe9a3ac8ed664e7e

Commit description:

parse_dcc() treats data_end as an inclusive end pointer, but its only
caller passes data_limit = ib_ptr + datalen, which points one past the
last valid byte.

The newline search loop iterates while tmp <= data_end, so when no
newline is present, *tmp is read at tmp == data_end, one byte beyond
the region filled by skb_header_pointer().

irc_buffer is kmalloc'd as MAX_SEARCH_SIZE + 1 bytes and datalen is
capped at MAX_SEARCH_SIZE, so the stray read does not fault.  The byte
is uninitialized or stale; if it contains an ASCII digit, simple_strtoul
will consume it and produce a wrong DCC IP or port in the conntrack
expectation.  The extra allocation byte is also a fragile guard: if the
cap or allocation size changes, this becomes a real out-of-bounds read.

Change the loop and its post-loop check to use strict less-than,
consistent with the caller's exclusive-end convention.  Update the
function comment accordingly.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/netfilter/nf_conntrack_irc.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=abb8c32b88ea3f46beb68c34fe9a3ac8ed664e7e

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80603 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80603

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:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
  The Best / paranoid CVSS score: 4.8

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).