CVE-2026-53385: vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-19 · updated 2026-08-17
Weakness: CWE-476

Description

In the Linux kernel, the following vulnerability has been resolved: vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write A KASAN null-ptr-deref was observed in vcs_notifier(): BUG: KASAN: null-ptr-deref in vcs_notifier+0x98/0x130 Read of size 2 at addr qmp_cmd_name: qmp_capabilities, arguments: {} The issue is a race condition in vcs_write(). When the console_lock is temporarily dropped (to copy data from userspace), the vc_data pointer obtained from vcs_vc() may become stale. After re-acquiring the lock, vcs_vc() is called again to re-validate the pointer. If the vc has been deallocated in the meantime, vcs_vc() returns NULL, and the while loop breaks (with written > 0). However, after the loop, vcs_scr_updated(vc) is still called with the now-NULL vc pointer, leading to a null pointer dereference in the notifier chain (vcs_notifier dereferences param->vc). Fix this by adding a NULL check for vc before calling vcs_scr_updated().

Affected products

Linux kernel: from 4.14.327 before 4.15; from 4.19.284 before 4.20; from 5.4.244 before 5.5; from 5.10.181 before 5.10.260; from 5.15.113 before 5.15.211; from 6.1.30 before 6.1.177 — fixed in 4.15, 4.20, 5.10.260, 5.15.211, 5.5, 6.1.177

How to fix

Upgrade to a fixed version: Linux kernel 4.15, 4.20, 5.10.260, 5.15.211. Check the vendor advisory for mitigations.

References

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