[CVE-2026-68119][MODERATE REGULAR] tcp: initialize standalone TCP-AO response padding

[CVE-2026-68119][MODERATE REGULAR] tcp: initialize standalone TCP-AO response padding

[AL-KERNEL]

CVE: CVE-2026-68119
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tcp: initialize standalone TCP-AO response padding
Commit: bbb7db8c74b0b5d17a695136f0f0806ecd0118f6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbb7db8c74b0b5d17a695136f0f0806ecd0118f6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68119
Analysis date: Mon, 10 Aug 2026 18:10:21 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline manual review recommended / below Important
Manual review required: YES

Summary:
TCP-AO standalone TCP responses may transmit 1 to 3 bytes of uninitialized padding after the AO MAC to a reachable remote peer, causing a small kernel memory disclosure without evidence of integrity impact, availability impact, or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-68119 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68119

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 REGULAR
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-2026-68119	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:H/I:N/A:N';CWE-908;*CWE-457;*CWE-200;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.9';DESCR 'TCP-AO standalone TCP responses can include uninitialized alignment padding after the AO MAC when the MAC length is not 4 byte aligned. These 1 to 3 padding bytes are part of the transmitted TCP header and may disclose small pieces of kernel memory from the response construction path to a remote peer. For the CVSS the PR:N is used because a remote attacker does not need a local account on the target, but reliable triggering requires access to a reachable TCP-AO protected endpoint and a configuration with an affected MAC length. The issue is network reachable in TCP-AO deployments, although TCP-AO is typically used in controlled routing or infrastructure networks rather than general public services. Impact is primarily confidentiality. No reliable integrity impact, availability impact, or privilege escalation primitive is visible from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / below Important (with actual score 4)  SKIP CVE-2026-68119 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: decde2586b34b99684faff1eab41e5c496c27fb6 YES  NO NO unknown 	MAYBE	REMOTE SIMPLEFIX NETWORK LINUS IPV6  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / below Important**

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  A remote peer that can reach a TCP-AO protected endpoint may receive standalone TCP responses containing the uninitialized padding bytes.

* Confidentiality impact plausible: +1
  The bug can disclose 1 to 3 bytes of uninitialized kernel stack or response-construction memory in transmitted TCP headers.

* Common networking core path or packet-processing path: +1
  The affected code is in TCP IPv4 and IPv6 response generation, though the vulnerable branch is limited to TCP-AO.

* No generic memory corruption: +0
  The patch only initializes padding before hashing and transmission. It does not show UAF, OOB write, double free, type confusion, arbitrary write, or lifetime corruption.

* No integrity or availability signal: +0
  No write primitive, privilege escalation path, crash, or persistent DoS is indicated.

* No rare subsystem penalty applied: 0
  TCP-AO is not commonly exposed like ordinary TCP services, but this is still a TCP networking path. The limited deployment is handled in reachability interpretation rather than subtracting score.

## 3. Reachability analysis

The bug can be triggered only when TCP-AO is configured and a remote peer can interact with the protected TCP endpoint. No local account is required on the target, so the practical PR interpretation is PR:N for CVSS-style reasoning. However, TCP-AO is usually deployed in controlled routing, infrastructure, or private network environments rather than exposed broadly to the public Internet. Namespaces and containers do not materially improve attacker reachability unless they can access or influence a TCP-AO protected connection.

Call-site confidence: high. The patch directly shows tcp_v4_send_ack() and tcp_v6_send_response() transmitting standalone TCP responses with TCP-AO options.

## 4. Severity interpretation

This behaves like a network-reachable information disclosure, not memory corruption and not privilege escalation. The leak size is very small, only 1 to 3 padding bytes per affected response, and exploitation depends on TCP-AO configuration and MAC length alignment. Realistic impact is confidentiality-only and likely Moderate, but it should not be blindly auto-closed because the disclosure is remote and occurs in kernel networking code.

## 5. One-sentence report phrase

TCP-AO standalone TCP responses may transmit 1 to 3 bytes of uninitialized padding after the AO MAC to a reachable remote peer, causing a small kernel memory disclosure without evidence of integrity impact, availability impact, or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable kernel information disclosure, even though the leak is small and configuration-dependent. Manual review should confirm TCP-AO exposure, affected MAC lengths, and whether repeated responses can disclose security-relevant data in the evaluated product.

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

Patch: tcp: initialize standalone TCP-AO response padding
Commit: bbb7db8c74b0b5d17a695136f0f0806ecd0118f6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbb7db8c74b0b5d17a695136f0f0806ecd0118f6

Commit description:

tcp_v4_send_ack() and tcp_v6_send_response() construct standalone TCP
responses with TCP-AO options.  The option length carries the actual MAC
length, but the TCP header length includes the option rounded up to a
four-byte boundary.

tcp_ao_hash_hdr() writes the MAC only.  Thus, when the MAC length is not
four-byte aligned, the one to three bytes after the MAC are left
uninitialized and may be transmitted.  For the normal TCP-AO hashing
mode, those bytes also have to be initialized before computing the MAC.

Initialize only the alignment padding in the TCP-AO branches, before
hashing the header.  Use TCPOPT_NOP, as in the normal TCP-AO output path.
This avoids adding work to non-AO TCP responses while preserving a valid
authenticated header.

Fixes: decde25 ("net/tcp: Add TCP-AO sign to twsk")
Fixes: da7dfaa ("net/tcp: Consistently align TCP-AO option in the header")
Cc: stable@vger.kernel.org
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260713105631.8616-1-zhaoyz24@mails.tsinghua.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/tcp_ipv4.c
  net/ipv6/tcp_ipv6.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=bbb7db8c74b0b5d17a695136f0f0806ecd0118f6

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

The original Linux kernel CVE announcement for CVE-2026-68119 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68119

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:N
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.9

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: unknown
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).