CyberSecBulletin
CVE-2026-31705NVD status: Modified

Linux: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-31705 is a critical-severity out-of-bounds write vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions ddbbc8b2a09dd2cfed90871313e3691ae1db08a2, ffbce350c6fd1e99116ea57383b9031717e36d3b, 98f3de6ef4efbd899348d333f0902dc4ff14380c 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 0.4% chance of exploitation within 30 days, which is low compared with other CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Update Linux to ddbbc8b2a09dd2cfed90871313e3691ae1db08a2 or ffbce350c6fd1e99116ea57383b9031717e36d3b or 98f3de6ef4efbd899348d333f0902dc4ff14380c or 790304c02bf9bd7b8171feda4294d6e62d32ae8f, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.16 or 6.2 or 6.6.136 or 6.12.84, whichever matches your release line, or a later version.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux9f297df20d93411c0b4ddad7f88ba04a7cd36e77 up to, but not including, ddbbc8b2a09dd2cfed90871313e3691ae1db08a2; e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to, but not including, ffbce350c6fd1e99116ea57383b9031717e36d3b; e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to, but not including, 98f3de6ef4efbd899348d333f0902dc4ff14380c; e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to, but not including, 790304c02bf9bd7b8171feda4294d6e62d32ae8f; e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to, but not including, 922d48fe8c19f388ffa2f709f33acaae4e408de2; e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to, but not including, 30010c952077a1c89ecdd71fc4d574c75a8f5617; f2283680a80571ca82d710bc6ecd8f8beac67d63; 6.1.71 up to, but not including, 6.1.175; and 2 more rangesddbbc8b2a09dd2cfed90871313e3691ae1db08a2, ffbce350c6fd1e99116ea57383b9031717e36d3b, 98f3de6ef4efbd899348d333f0902dc4ff14380c, 790304c02bf9bd7b8171feda4294d6e62d32ae8f, 922d48fe8c19f388ffa2f709f33acaae4e408de2, 30010c952077a1c89ecdd71fc4d574c75a8f5617
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel5.15.145 up to, but not including, 5.16; 6.1.71 up to, but not including, 6.2; 6.6 up to, but not including, 6.6.136; 6.7 up to, but not including, 6.12.84; 6.13 up to, but not including, 6.18.25; 6.19 up to, but not including, 7.0.25.16, 6.2, 6.6.136, 6.12.84, 6.18.25, 7.0.2

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
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
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:N/AC:L/PR:N/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: ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment smb2_get_ea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buf_free_len is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space. When the EA value exactly fills the remaining buffer (buf_free_len == 0 after value subtraction), the alignment memset writes 1-3 NUL bytes past the buf_free_len boundary. In compound requests where the response buffer is shared across commands, the first command (e.g., READ) can consume most of the buffer, leaving a tight remainder for the QUERY_INFO EA response. The alignment memset then overwrites past the physical kvmalloc allocation into adjacent kernel heap memory. Add a bounds check before the alignment memset to ensure buf_free_len can accommodate the padding bytes. This is the same bug pattern fixed by commit beef2634f81f ("ksmbd: fix potencial OOB in get_file_all_info() for compound requests") and commit fda9522ed6af ("ksmbd: fix OOB write in QUERY_INFO for compound requests"), both of which added bounds checks before unconditional writes in QUERY_INFO response handlers.

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. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Write vulnerabilities

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