From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98838][MODERATE REGULAR] vt: skip screen update for DEC alignment test on backgroup consoles Date: Sat, 24 Oct 2026 12:44:04 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98838 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 985c000b046ca4ee11ee34ef85db500c569ef6e8 List-Id: CVE: CVE-2026-98838 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: vt: skip screen update for DEC alignment test on backgroup consoles Commit: 985c000b046ca4ee11ee34ef85db500c569ef6e8 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=985c000b046ca4ee11ee34ef85db500c569ef6e8 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98838 Analysis date: Sat, 24 Oct 2026 12:44:04 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A privileged-looking background-console rendering sequence can cause a slab OOB read, with possible pixel-mediated disclosure but no demonstrated write, UAF, or reliable host crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98838 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98838 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98838 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98838 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-125;*CWE-20;*CWE-664;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '6.1';DESCR 'A background virtual console can execute the DEC alignment test through ESC hash 8 after its font dimensions were changed without resizing the rotated framebuffer buffer. The resulting do_update_region call can make fb_pad_aligned_buffer read beyond the slab allocation because this control path lacked the normal con_should_update check. The demonstrated primitive is an out of bounds read rather than an out of bounds write or UAF. Adjacent bytes may influence framebuffer output and a hardened configuration may turn the KASAN warning into a kernel panic, but arbitrary memory modification or privilege escalation is not established. For the CVSS the PR:H value reflects that KDFONTOP font replacement and global fbcon rotation normally require privileged console administration. For the CVSS the PR:L value in the paranoid vector covers deployments that delegate limited console control to a service or constrained administrator. The issue is local and requires a specific multi console framebuffer configuration rather than network reachability. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 6.1 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE READ KASAN OOB PRINTF-TTY HARDWARE LINUS TEST V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 1. * Conservative score: 1; no floor or cap applied. * Raw paranoid score: 2. * Paranoid score: 2; no floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * **+1 limited OOB read:** The mismatched background-console font dimensions make `fb_pad_aligned_buffer()` read beyond the allocated rotated framebuffer buffer. * **Paranoid +1 plausible confidentiality path:** The bytes read feed framebuffer rendering, so adjacent slab data could influence visible pixels. Actual recovery of sensitive bytes is not demonstrated. * **No OOB-write or B5-R credit:** The KASAN report explicitly identifies a one-byte read. There is no retry-accumulated index, heap write, or later consumption of corrupted structured state. * **No crash point:** KASAN reports a warning; panic requires an additional hardened/panic configuration and is not shown as reliable. * No UAF, arbitrary write, controlled reclaim, authorization bypass, integrity impact, or privilege escalation is established. * No privilege penalty applied because the exact effective privilege checks for the complete sequence are not supplied. 3. Reachability analysis The demonstrated sequence requires access to two virtual consoles, `KDFONTOP` font changes, framebuffer-console rotation through sysfs, and writing `ESC # 8` to the background console. The reproducer runs as UID 0, and the supplied summary says font replacement and global rotation normally require privileged console administration. However, the exact capability and delegation rules are absent, so neither effective host-admin necessity nor below-host-admin reachability is proven. No namespace-scoped path is shown. The setup requires fbcon, multiple VCs, and rotation, but no timing race or special physical hardware. 4. Primitive and severity reading The primitive is a bounded-at-point-of-fault slab OOB read from an undersized rotated rendering buffer caused by bypassing `con_should_update()` for a background VC. This is invalid rendering state, not active structured-state corruption, a UAF, or an OOB write. The shown effect is a KASAN warning; visual disclosure or panic remains plausible but unconfirmed. Therefore it is CLASS_C, not an Important-preserving B5-R candidate. Automatic downgrade is allowed, though manual validation of console permissions and framebuffer observability is advisable. 5. One-sentence report phrase A privileged-looking background-console rendering sequence can cause a slab OOB read, with possible pixel-mediated disclosure but no demonstrated write, UAF, or reliable host crash. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm the exact console/sysfs privilege requirements and whether adjacent slab bytes can be observably reconstructed from framebuffer output. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vt: skip screen update for DEC alignment test on backgroup consoles Commit: 985c000b046ca4ee11ee34ef85db500c569ef6e8 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=985c000b046ca4ee11ee34ef85db500c569ef6e8 Commit description: [BUG] Recently, we encountered a KASAN warning as follows: BUG: KASAN: slab-out-of-bounds in fb_pad_aligned_buffer+0x11f/0x140 Read of size 1 at addr ff1100015fd9f6a4 by task tty_fbcon_oob/1239 CPU: 7 UID: 0 PID: 1239 Comm: tty_fbcon_oob Not tainted 7.3.0-rc1 #100 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014 Call Trace: ... kasan_report+0xf0/0x120 fb_pad_aligned_buffer+0x11f/0x140 ccw_putcs+0x86c/0xa80 fbcon_putcs+0x338/0x410 do_update_region+0x21d/0x450 do_con_write+0x1e0e/0x4880 con_write+0x13/0x80 n_tty_write+0x374/0x1010 file_tty_write.isra.0+0x404/0x7a0 ... reproduce: 1) open /dev/tty0, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET, op.width = 8 and op.height = 16 (visible VC1) 2) open /dev/tty1, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET, op.width = 28 and op.height = 24 (invisible VC2) 3) echo 3 > /sys/devices/virtual/graphics/fbcon/rotate_all 4) write EShash8(esc hash8) to tty1 [CAUSE] All VCs render to the framebuffer. setfont only modifies the target VC's font without resizing the framebuffer backing buffer (par->rotated.buf); the buffer is only resized for the visible VC (fbcon_do_set_font -> ... -> vc_do_resize -> update_screen). This relies on the con_should_update() check performed before every update_region(). However, the ESC # 8 path (do_con_trol -> do_update_region) omits the con_should_update() check. After changing the font size of an invisible VC, do_update_region() fills using the new font size against a buffer that was never resized, causing an out-of-bounds access. [FIX] Only push the update when the console is visible and not blanked, add the con_should_update() check in the do_con_trol() like every other call site of do_update_region() (update_region(), invert_screen(), ...). Fixes: 1da177e ("Linux-2.6.12-rc2") Cc: stable Signed-off-by: Zizhi Wo Link: https://patch.msgid.link/20260905064337.3083103-1-wozizhi@huaweicloud.com Signed-off-by: Greg Kroah-Hartman Changed files: drivers/tty/vt/vt.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=985c000b046ca4ee11ee34ef85db500c569ef6e8 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98838 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98838 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:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS score: 6.1 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: 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).