From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68278][IMPORTANT] drm/dp/mst: fix buffer overflows in sideband chunk accumulation Date: Mon, 10 Aug 2026 10:34:50 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68278 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 53937a2787d29c7a460e984dc4f20ff6ac91dc65 List-Id: CVE: CVE-2026-68278 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: drm/dp/mst: fix buffer overflows in sideband chunk accumulation Commit: 53937a2787d29c7a460e984dc4f20ff6ac91dc65 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=53937a2787d29c7a460e984dc4f20ff6ac91dc65 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68278 Analysis date: Mon, 10 Aug 2026 10:34:50 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A malicious DisplayPort MST monitor, hub, or dock can send malformed sideband reply chunks that trigger OOB reads and OOB writes in drm_dp_sideband_append_payload(), causing kernel memory corruption and at least a host DoS, with possible privilege escalation in the worst case. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68278 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68278 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-2026-68278 IMPORTANT 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:H/I:H/A:H';*CWE-787;CWE-125;CWE-191;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H';BEST CVSS score: '6.8';DESCR 'A kernel memory corruption issue exists in the DP MST sideband reply parser because device controlled msg_len values can drive invalid chunk accumulation. A malicious DP MST monitor, hub, or dock can send malformed sideband reply chunks that cause an out of bounds read from chunk(48), an out of bounds write past chunk(48), or an out of bounds write past msg(256). For the CVSS the PR:N is used because no host account or kernel privilege is required once the attacker can provide or control the physical DP MST device. The issue is not IP network reachable and requires access to a physical DisplayPort MST connection or a malicious device already attached to the target. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES OOB HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Firmware-mediated external influence: +1. The malformed data is supplied by a DP MST device over the physical DisplayPort sideband channel. * Memory corruption, Strong corruption primitive: +2. The patch prevents concrete OOB writes past chunk(48) and msg(256), plus an OOB read caused by u8 underflow. * Reliable kernel crash / strong DoS: +1. Kernel memory corruption in a DRM parser can realistically crash the host. * Confidentiality impact plausible: +1. OOB read and memory corruption make limited disclosure plausible, although no direct read-back primitive is shown. * Integrity impact plausible: +1. Device-controlled malformed chunks can drive OOB writes into adjacent kernel object fields. * Physical-only or rare hardware-only condition: -2. Triggering requires a malicious or compromised physical DP MST monitor, hub, dock, or equivalent device. Conservative total: 5 Paranoid additional signals: * Privilege escalation plausible: +2 instead of weak LPE concern. This is not a NULL deref or validation-only bug. The patch fixes concrete kernel OOB writes with device-influenced data, so kernel code execution or privilege escalation is technically defensible in a malicious peripheral model. * Broad/default/common subsystem exposure: +1. DisplayPort MST support is common on laptops, docks, monitors, and workstation setups, although exposure still requires physical device presence. Paranoid total: 7 ## 3. Reachability analysis The attacker needs control over a DP MST device that can send forged sideband reply messages. This is not IP network reachable and should not be treated as a remote network vulnerability. No local Linux account is required once the malicious device is attached, so PR is effectively none in the device attack model. User interaction depends on scenario. Connecting a malicious dock or monitor is UI:R, while an already attached compromised device or attacker-accessible physical port can be modeled as UI:N for paranoid scoring. Namespaces and containers do not materially reduce the trigger requirement because the vulnerable parser runs in the host kernel DRM stack and is driven by physical display hardware. The path is configuration and hardware dependent, but DisplayPort MST is common enough that this should not be auto-closed as rare-only. Call-site confidence: high. The vulnerable function and bounds checks are directly present in the patch. ## 4. Severity interpretation This behaves more like an Important candidate than an ordinary Moderate because the patch fixes concrete OOB read and OOB write conditions in kernel memory. Realistic exploitation is constrained by physical-device requirements, which keeps the conservative score at Actionable Moderate. The paranoid score is higher because the corruption is device-controlled and occurs in a trusted kernel parser, making manual analysis necessary. The theoretical risk includes kernel memory corruption and possible privilege escalation or code execution. The realistic demonstrated impact from the patch is malformed DP MST sideband data causing memory corruption and likely kernel crash. ## 5. One-sentence report phrase A malicious DisplayPort MST monitor, hub, or dock can send malformed sideband reply chunks that trigger OOB reads and OOB writes in drm_dp_sideband_append_payload(), causing kernel memory corruption and at least a host DoS, with possible privilege escalation in the worst case. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: concrete kernel OOB writes are present, input is attacker-controlled through a physical peripheral protocol, and the affected parser is in a host kernel driver path. This should not be auto-closed despite the physical-access requirement. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: drm/dp/mst: fix buffer overflows in sideband chunk accumulation Commit: 53937a2787d29c7a460e984dc4f20ff6ac91dc65 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=53937a2787d29c7a460e984dc4f20ff6ac91dc65 Commit description: drm_dp_sideband_append_payload() has three related bugs when processing device-provided sideband reply data: 1. Zero-length curchunk_len underflow: msg_len is a 6-bit field taken directly from the DP sideband header. If a device sends msg_len=0, curchunk_len is set to zero. The condition (curchunk_idx >= curchunk_len) is immediately true, and curchunk_len-1 wraps to 255 (u8 underflow). drm_dp_msg_data_crc4() reads 255 bytes from chunk[48], then memcpy() writes 255 bytes into msg[], both far out of bounds. 2. chunk[48] overflow: curchunk_len can reach 63 (6-bit field). chunk[] is only 48 bytes. Multi-iteration payload assembly appends 16-byte blocks until curchunk_idx reaches curchunk_len, writing up to 15 bytes past the end of chunk[] into msg[]. 3. msg[256] overflow: each chunk contributes (curchunk_len-1) bytes to msg[]. No check ensures curlen + (curchunk_len-1) stays within msg[256], so the memcpy can spill into adjacent struct fields. All three are reachable from any DP MST device that can forge sideband reply messages on a physical connection. Fixes: ad7f8a1 ("drm/helper: add Displayport multi-stream helper (v0.6)") Cc: # v3.17+ Signed-off-by: Ashutosh Desai Reviewed-by: Lyude Paul Signed-off-by: Lyude Paul Link: https://patch.msgid.link/20260410041901.2438960-1-ashutoshdesai993@gmail.com Signed-off-by: Greg Kroah-Hartman 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=53937a2787d29c7a460e984dc4f20ff6ac91dc65 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68278 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68278 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:R/S:U/C:H/I:H/A:H The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.8 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: 5 Paranoid ActionableScore: 7 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).