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CVE-2026-98840

Linux: vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF

Linux LinuxOperating systems
Open in ThreatlineRecord JSON
CVSS
NoneNot scored
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.17%Chance of exploitation activity in the next 30 days, higher than 5% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in1485a3dd97ab1af2605243cabe6b604546d46dd1Also 233a2e190b12884d186027d0b86d43a48799b69c, 9dfcadc5e003fb250dd471db90144bd5366140e9 and 9 moreCVE List
Published18 Oct 2026Updated 21 Oct 2026CVE List

What fixes it

  • 1485a3dd97ab1af2605243cabe6b604546d46dd1LinuxCVE List
  • 233a2e190b12884d186027d0b86d43a48799b69cLinuxCVE List
  • 9dfcadc5e003fb250dd471db90144bd5366140e9LinuxCVE List
  • 226bd5603371cd9f6642cbb9e9a677f445de3530LinuxCVE List
  • 6.6.160LinuxCVE List
  • 6.12.113LinuxCVE List
Show all 12 fixed versions

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

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().

Text from CVE List

Affected versions 25

  • Linuxaffected: 8232fca738011ca2ec865b46ec721d1796dc0580 before c073d01f6f5367c3a4f07efd507274ed0d03acd0CVE List
  • Linuxaffected: 73049768ad57145acd337102c5aa3c788e6642c8 before 1485a3dd97ab1af2605243cabe6b604546d46dd1CVE List
  • Linuxaffected: 7cc3dd79777f6ae4625ec37e84dd18a26dc88bde before 233a2e190b12884d186027d0b86d43a48799b69cCVE List
  • Linuxaffected: a287620312dc6dcb9a093417a0e589bf30fcf38a before 9dfcadc5e003fb250dd471db90144bd5366140e9CVE List
  • Linuxaffected: a287620312dc6dcb9a093417a0e589bf30fcf38a before 226bd5603371cd9f6642cbb9e9a677f445de3530CVE List
  • Linuxaffected: 43a6281790273c1b0a9ab76609ff0245b968f1e6CVE List
  • Linuxaffected: b6bbb85cf45bf0b070e741997fe0af3a772c5ad5CVE List
  • Linuxaffected: ff4806202749a51938236214adc0281481a57366CVE List
  • Linuxaffected: 74be188eb2dc1c99d63986167b9a67d415fe7326CVE List
  • Linuxaffected: 09a43e81279b8da15526da09877134b8bcf618b0CVE List
  • Linuxaffected: 6.6.144 before 6.6.160CVE List
  • Linuxaffected: 6.12.95 before 6.12.113CVE List
  • Linuxaffected: 6.18.37 before 6.18.56CVE List
  • Linuxaffected: 5.10.260 before 5.11CVE List
  • Linuxaffected: 5.15.211 before 5.16CVE List
  • Linuxaffected: 6.1.177 before 6.2CVE List
  • Linuxaffected: 7.0.14 before 7.1CVE List
  • Linuxaffected: 7.1.2 before 7.2CVE List
  • Linuxaffected: 7.2CVE List
  • Linuxunaffected: all versions before 7.2CVE List
  • Linuxunaffected: 6.6.160 through 6.6.*CVE List
  • Linuxunaffected: 6.12.113 through 6.12.*CVE List
  • Linuxunaffected: 6.18.56 through 6.18.*CVE List
  • Linuxunaffected: 7.2.10 through 7.2.*CVE List
  • Linuxunaffected: 7.3CVE List

References 5