Linux Kernel up to 6.12.112/6.18.55/7.2.9/7.3-rc5 vc_screen vcs_write vc_num use after free

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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9.5$5k-$25k0.00

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.12.112/6.18.55/7.2.9/7.3-rc5. It has been declared as very critical. Affected by this issue is the function vcs_write of the component vc_screen. Executing a manipulation of the argument vc_num can lead to use after free. This vulnerability is registered as CVE-2026-98840. It is possible to launch the attack remotely. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability classified as very critical was found in Linux Kernel up to 6.12.112/6.18.55/7.2.9/7.3-rc5. This vulnerability affects the function vcs_write of the component vc_screen. The manipulation of the argument vc_num with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF The reload of 'vc' added by commit 8fb9ea65c9d1 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF") sits after the 'if (ret)' block, so the copy-failure break path exits the loop without reloading vc. If the vc was kfree()'d via vc_port_destruct during the unlocked copy_from_user() window, the post-loop 'if (written && vc) vcs_scr_updated(vc)' is reached with a stale non-NULL vc. The '&& vc' guard from commit a287620312dc ("vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write") only handles the NULL case, not this stale-non-NULL case; vcs_notifier() then reads param->vc->vc_num from freed memory: BUG: KASAN: slab-use-after-free in vcs_notifier+0x7c/0xd0 Read of size 2 at addr ffff888007149190 Call Trace: vcs_notifier+0x7c/0xd0 atomic_notifier_call_chain+0x70/0xa0 vcs_scr_updated+0x77/0xa0 vcs_write+0x71b/0x7e0 Allocated by task: vc_allocate -> con_install -> tty_open Freed by task: kfree <- vt_ioctl (VT_DISALLOCATE -> vc_port_destruct) Move the reload to immediately after console_lock(), before 'if (ret)', so every break path below passes a fresh vc to the post-loop vcs_scr_updated().

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-98840 since 09/25/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 10/18/2026).

Upgrading to version 6.12.113, 6.18.56, 7.2.10 or 7.3-rc6 eliminates this vulnerability. Applying the patch 1485a3dd97ab1af2605243cabe6b604546d46dd1/233a2e190b12884d186027d0b86d43a48799b69c/9dfcadc5e003fb250dd471db90144bd5366140e9/226bd5603371cd9f6642cbb9e9a677f445de3530 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

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Name

Version

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 9.9
VulDB Meta Temp Score: 9.5

VulDB Base Score: 9.9
VulDB Temp Score: 9.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.12.113/6.18.56/7.2.10/7.3-rc6
Patch: 1485a3dd97ab1af2605243cabe6b604546d46dd1/233a2e190b12884d186027d0b86d43a48799b69c/9dfcadc5e003fb250dd471db90144bd5366140e9/226bd5603371cd9f6642cbb9e9a677f445de3530

Timelineinfo

09/25/2026 CVE reserved
10/18/2026 +23 days Advisory disclosed
10/18/2026 +0 days VulDB entry created
10/18/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-98840 (🔒)
GCVE (CVE): GCVE-0-2026-98840
GCVE (VulDB): GCVE-100-421840

Entryinfo

Created: 10/18/2026 18:23
Changes: 10/18/2026 18:23 (60)
Complete: 🔍
Cache ID: 216::103

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