[CVE-2026-68279][MODERATE REGULAR] drm/dp/mst: fix OOB reads in remote DPCD/I2C sideband reply parsers

[CVE-2026-68279][MODERATE REGULAR] drm/dp/mst: fix OOB reads in remote DPCD/I2C sideband reply parsers

[AL-KERNEL]

CVE: CVE-2026-68279
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/dp/mst: fix OOB reads in remote DPCD/I2C sideband reply parsers
Commit: 22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68279
Analysis date: Mon, 10 Aug 2026 20:33:57 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / manual review recommended
Manual review required: YES

Summary:
A malicious DisplayPort MST hub or monitor can send malformed remote DPCD or I2C sideband replies that cause the kernel DRM MST parser to read beyond the received payload, potentially exposing limited stale buffer data or causing DoS in some configurations.

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

The original Linux kernel CVE announcement for CVE-2026-68279 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68279

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-2026-68279	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.2';DESCR 'A malformed DisplayPort MST sideband reply can make the remote DPCD/I2C reply parsers copy num_bytes from raw msg without first proving that idx plus num_bytes is within the received curlen. A malicious or misbehaving MST hub or monitor can therefore trigger an out of bounds read from kernel parser memory by returning a reply whose advertised byte count is larger than the remaining payload. For the CVSS the PR:N is used because the attacker does not need privileges on the target host once they control the attached MST device or the DP MST path. The issue is not network reachable over IP and is better modeled as physical access to the display path. Impact is primarily limited confidentiality exposure and possible denial of service. There is no clear integrity impact or privilege escalation primitive because the patch shows an out of bounds read before memcpy, not an out of bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / manual review recommended (with actual score 2)	YES	OOB SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. A malicious or faulty DisplayPort MST hub or monitor can influence the sideband reply payload.
* Confidentiality impact plausible: +1. The parser can copy bytes beyond the received sideband payload, potentially exposing stale kernel parser buffer contents.
* Physical-only or rare hardware-only condition: -2. Triggering requires control of the DisplayPort MST device or display path, not remote network access or ordinary local code execution.
* Weak corruption: +0. This is a read-only OOB condition, not an OOB write, UAF, double free, type confusion, or refcount takeover.

Paranoid additional signal:

* Availability impact realistic: +1. A malformed hardware-facing parser input may cause parser failure, warning, or crash in hardened/debug configurations, but the patch does not show a strong crash primitive.

## 3. Reachability analysis

The attacker must control or emulate a malicious DisplayPort MST hub, monitor, or device on the DP MST path. No local user privileges on the host are required once the malicious device is attached, so this is not PR:L in the usual local-user sense, but it is also not network reachable. Namespaces and containers do not materially change reachability because the trigger is in the physical display hardware path. The affected code is present in the DRM DisplayPort MST helper path and can be reached on systems using DP MST, but the realistic exposure is workstation or laptop display connectivity rather than server-side default remote attack surface.

Call-site confidence: medium. The patch shows the vulnerable parser and memcpy sites directly, but not the full downstream visibility of copied reply bytes.

## 4. Severity interpretation

This behaves more like an ordinary Moderate or Low-like hardware-facing memory safety issue than an Important-class kernel vulnerability. Theoretical confidentiality impact is plausible because attacker-controlled length fields can cause OOB reads from the parser buffer. Realistic exploitation evidence is limited because the bug is read-only, physically scoped, and does not show an overwrite, UAF reclaim, callback corruption, or privilege escalation primitive. The paranoid score remains low because the bug class must not be upgraded from limited OOB read into memory corruption with integrity impact.

## 5. One-sentence report phrase

A malicious DisplayPort MST hub or monitor can send malformed remote DPCD or I2C sideband replies that cause the kernel DRM MST parser to read beyond the received payload, potentially exposing limited stale buffer data or causing DoS in some configurations.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This should not be treated as an Important candidate by default, but manual review is reasonable because it is an attacker-controlled kernel OOB read in a hardware-facing parser and the exact disclosure or crash behavior depends on surrounding buffer lifetime and downstream handling.

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

Patch: drm/dp/mst: fix OOB reads in remote DPCD/I2C sideband reply parsers
Commit: 22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2

Commit description:

drm_dp_sideband_parse_remote_dpcd_read() reads num_bytes from the raw
message and then unconditionally does:

  memcpy(bytes, &raw->msg[idx], num_bytes);

without checking that idx + num_bytes <= raw->curlen. raw->msg[] is
256 bytes; if a malicious or misbehaving MST hub sets num_bytes larger
than the remaining payload, the memcpy reads past the received data
into whatever follows in raw->msg[].

drm_dp_sideband_parse_remote_i2c_read_ack() has the same flaw (noted
with a /* TODO check */ comment since the code was introduced).

Fix both functions by using a single combined check
(idx + num_bytes > curlen) before each memcpy. Since num_bytes is u8,
it is always >= 0, so this strictly subsumes the simpler idx > curlen
form and no separate step is needed.

Fixes: ad7f8a1 ("drm/helper: add Displayport multi-stream helper (v0.6)")
Cc: <stable@vger.kernel.org> # v3.17+
Signed-off-by: Ashutosh Desai <ashutoshdesai993@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
[added missing fixes tag]
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20260510201733.2882224-1-ashutoshdesai993@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/display/drm_dp_mst_topology.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=22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2

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

The original Linux kernel CVE announcement for CVE-2026-68279 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68279

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.2

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: 1
  Paranoid ActionableScore: 2

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).