CyberSecBulletin
CVE-2026-31772NVD status: Modified

Linux: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-31772 is a high-severity out-of-bounds write vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions f5d446624345d309e7a4a1b27ea9f028d6a8c5d9, aba0aea354015794e8312dd7efe726967e58aefe, eaf32002ca7b1ba51c9f140991fd9febe6de79f0 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.14% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to f5d446624345d309e7a4a1b27ea9f028d6a8c5d9 or aba0aea354015794e8312dd7efe726967e58aefe or eaf32002ca7b1ba51c9f140991fd9febe6de79f0 or bc39a094730ce062fa034a529c93147c096cb488, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.12 or 6.12.81 or 6.18.22 or 6.19.12, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux91d19383b7ed035e22165ae5c836e50bb9f95fbe up to, but not including, f5d446624345d309e7a4a1b27ea9f028d6a8c5d9; 42ecf1947135110ea08abeaca39741636f9a2285 up to, but not including, aba0aea354015794e8312dd7efe726967e58aefe; 42ecf1947135110ea08abeaca39741636f9a2285 up to, but not including, eaf32002ca7b1ba51c9f140991fd9febe6de79f0; 42ecf1947135110ea08abeaca39741636f9a2285 up to, but not including, bc39a094730ce062fa034a529c93147c096cb488; 8958e1cee4e2eac1a5b825caa4dd96ce9ed975dd; 6.12.2 up to, but not including, 6.12.81; 6.11.11 up to, but not including, 6.12; 6.13f5d446624345d309e7a4a1b27ea9f028d6a8c5d9, aba0aea354015794e8312dd7efe726967e58aefe, eaf32002ca7b1ba51c9f140991fd9febe6de79f0, bc39a094730ce062fa034a529c93147c096cb488, 6.12.81, 6.12
LinuxLinux Kernel6.11.11 up to, but not including, 6.12; 6.12.2 up to, but not including, 6.12.81; 6.13.1 up to, but not including, 6.18.22; 6.19 up to, but not including, 6.19.12; 6.13; 7.06.12, 6.12.81, 6.18.22, 6.19.12

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync hci_le_big_create_sync() uses DEFINE_FLEX to allocate a struct hci_cp_le_big_create_sync on the stack with room for 0x11 (17) BIS entries. However, conn->num_bis can hold up to HCI_MAX_ISO_BIS (31) entries — validated against ISO_MAX_NUM_BIS (0x1f) in the caller hci_conn_big_create_sync(). When conn->num_bis is between 18 and 31, the memcpy that copies conn->bis into cp->bis writes up to 14 bytes past the stack buffer, corrupting adjacent stack memory. This is trivially reproducible: binding an ISO socket with bc_num_bis = ISO_MAX_NUM_BIS (31) and calling listen() will eventually trigger hci_le_big_create_sync() from the HCI command sync worker, causing a KASAN-detectable stack-out-of-bounds write: BUG: KASAN: stack-out-of-bounds in hci_le_big_create_sync+0x256/0x3b0 Write of size 31 at addr ffffc90000487b48 by task kworker/u9:0/71 Fix this by changing the DEFINE_FLEX count from the incorrect 0x11 to HCI_MAX_ISO_BIS, which matches the maximum number of BIS entries that conn->bis can actually carry.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Write vulnerabilities

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