Linux Kernel vc_screen UAF via stale vc pointer in vcs_write
CVE-2026-98840 Published on October 18, 2026
vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF
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().
Products Associated with CVE-2026-98840
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Affected Versions
Linux:- Version 73049768ad57145acd337102c5aa3c788e6642c8 and below 1485a3dd97ab1af2605243cabe6b604546d46dd1 is affected.
- Version 7cc3dd79777f6ae4625ec37e84dd18a26dc88bde and below 233a2e190b12884d186027d0b86d43a48799b69c is affected.
- Version a287620312dc6dcb9a093417a0e589bf30fcf38a and below 9dfcadc5e003fb250dd471db90144bd5366140e9 is affected.
- Version a287620312dc6dcb9a093417a0e589bf30fcf38a and below 226bd5603371cd9f6642cbb9e9a677f445de3530 is affected.
- Version 43a6281790273c1b0a9ab76609ff0245b968f1e6 is affected.
- Version b6bbb85cf45bf0b070e741997fe0af3a772c5ad5 is affected.
- Version ff4806202749a51938236214adc0281481a57366 is affected.
- Version 8232fca738011ca2ec865b46ec721d1796dc0580 is affected.
- Version 74be188eb2dc1c99d63986167b9a67d415fe7326 is affected.
- Version 09a43e81279b8da15526da09877134b8bcf618b0 is affected.
- Version 6.12.95 and below 6.12.113 is affected.
- Version 6.18.37 and below 6.18.56 is affected.
- Version 5.10.260 and below 5.11 is affected.
- Version 5.15.211 and below 5.16 is affected.
- Version 6.1.177 and below 6.2 is affected.
- Version 6.6.144 and below 6.7 is affected.
- Version 7.0.14 and below 7.1 is affected.
- Version 7.1.2 and below 7.2 is affected.
- Version 7.2 is affected.
- Before 7.2 is unaffected.
- Version 6.12.113, <= 6.12.* is unaffected.
- Version 6.18.56, <= 6.18.* is unaffected.
- Version 7.2.10, <= 7.2.* is unaffected.
- Version 7.3-rc6, <= * is unaffected.