CyberSecBulletin
CVE-2026-63923NVD status: Analyzed

Linux: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-63923 is a high-severity out-of-bounds write vulnerability in Linux, with a CVSS 3.1 base score of 8.8 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 4467fa514482bbce82f73788943c815f3d126ab3, 68be0260e2a02ff9b18a8678d5f8d1715fa20138, 2156a29aecfffa2eb7c558255690084efbe9f3b0 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 0.17% 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 4467fa514482bbce82f73788943c815f3d126ab3 or 68be0260e2a02ff9b18a8678d5f8d1715fa20138 or 2156a29aecfffa2eb7c558255690084efbe9f3b0, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.18.42 or 7.0.12, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxb8fea84a0468404fe3b3327ad54d583950be9dec up to, but not including, 4467fa514482bbce82f73788943c815f3d126ab3; b8fea84a0468404fe3b3327ad54d583950be9dec up to, but not including, 68be0260e2a02ff9b18a8678d5f8d1715fa20138; b8fea84a0468404fe3b3327ad54d583950be9dec up to, but not including, 2156a29aecfffa2eb7c558255690084efbe9f3b0; 6.134467fa514482bbce82f73788943c815f3d126ab3, 68be0260e2a02ff9b18a8678d5f8d1715fa20138, 2156a29aecfffa2eb7c558255690084efbe9f3b0
LinuxLinux Kernel6.13 up to, but not including, 6.18.42; 6.19 up to, but not including, 7.0.12; 7.16.18.42, 7.0.12

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
ChangedThe attack can reach beyond the vulnerable component into other systems.
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:C/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: octeontx2-af: validate body pcifunc in rvu_mbox_handler_rep_event_notify rvu_mbox_handler_rep_event_notify() in drivers/net/ethernet/marvell/ octeontx2/af/rvu_rep.c queues a sender-controlled REP_EVENT_NOTIFY request body verbatim, and rvu_rep_up_notify() then forwards event->pcifunc (the nested body field, distinct from the AF-normalised header pcifunc) into rvu_get_pfvf(), rvu_get_pf() and the AF->PF mailbox device index without any bounds check. A VF attached to a PF that has been put into switchdev representor mode reaches this path: the VF mailbox handler otx2_pfvf_mbox_handler() forwards every message id including MBOX_MSG_REP_EVENT_NOTIFY to AF without an allowlist, and the AF dispatcher rewrites only msg->pcifunc, leaving struct rep_event::pcifunc attacker-controlled. The sibling rvu_mbox_handler_esw_cfg() refuses requests whose header pcifunc is not rvu->rep_pcifunc; this handler has no equivalent gate. An out-of-range body pcifunc selects an &rvu->pf[]/&rvu->hwvf[] element past the allocated array and, for RVU_EVENT_MAC_ADDR_CHANGE, turns into a six-byte attacker-chosen OOB ether_addr_copy() target inside the queued worker; KASAN reports a slab-out-of-bounds write in rvu_rep_wq_handler. Reject malformed requests at the handler entry by gating on is_pf_func_valid(), which is already the canonical PF/VF range check in this driver; expose it via rvu.h so callers in rvu_rep.c can use it instead of open-coding the same range arithmetic.

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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