CyberSecBulletin
CVE-2026-63920NVD status: Analyzed

Linux: Out-of-bounds Read

Published Updated By the CyberSecBulletin desk

CVE-2026-63920 is a high-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 7.1 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 81394827dfb72772c50d0ae3bdfa094428a5d76d, 931b4a1f13408c2507719890f78f7227c34a0282, 08464413e628803bd10cb1df68d0138665f2f885 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 81394827dfb72772c50d0ae3bdfa094428a5d76d or 931b4a1f13408c2507719890f78f7227c34a0282 or 08464413e628803bd10cb1df68d0138665f2f885 or a29768d56eb3798c052ad3281b05596e695a17af, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.259 or 5.15.210 or 6.1.176 or 6.6.143, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 81394827dfb72772c50d0ae3bdfa094428a5d76d; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 931b4a1f13408c2507719890f78f7227c34a0282; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 08464413e628803bd10cb1df68d0138665f2f885; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, a29768d56eb3798c052ad3281b05596e695a17af; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 0d330eff318c0f44d4fb0ad2c2aef38f87f24c90; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, a35daeabb433686234b010ebf7b53778dbd6c9b8; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, eb18a1b1644e4cad978df2131e2bb9a2e6886992; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, dd433671fef381fdaf7b530c631e6b782d66e224; and 1 more ranges81394827dfb72772c50d0ae3bdfa094428a5d76d, 931b4a1f13408c2507719890f78f7227c34a0282, 08464413e628803bd10cb1df68d0138665f2f885, a29768d56eb3798c052ad3281b05596e695a17af, 0d330eff318c0f44d4fb0ad2c2aef38f87f24c90, a35daeabb433686234b010ebf7b53778dbd6c9b8
LinuxLinux Kernel2.6.12.1 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 2.6.12; and 1 more ranges5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35

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
NoneNothing can be modified.
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:N/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: ipv6: validate extension header length before copying to cmsg ip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR} cmsgs (and their IPV6_2292* legacy counterparts) by trusting the on-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length. The length was validated only at parse time (ipv6_parse_hopopts(), etc.). An nftables payload-write expression can rewrite hdrlen after parsing and before the skb reaches recvmsg; the write itself is in-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040 bytes from an 8-byte header. nftables is reachable from an unprivileged user namespace, so this is an unprivileged slab-out-of-bounds read: BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540 put_cmsg+0x3ac/0x540 udpv6_recvmsg+0xca0/0x1250 sock_recvmsg+0xdf/0x190 ____sys_recvmsg+0x1b1/0x620 Add ipv6_get_exthdr_len() which validates that at least two bytes are accessible before reading the hdrlen field, then checks the computed length against skb_tail_pointer(skb), returning 0 on failure. Extension headers are kept in the linear skb area by pskb_may_pull() during input, so skb_tail_pointer() is the correct bound. Use ipv6_get_exthdr_len() at all non-AH call sites: the five standalone cmsg blocks (HbH, 2292HbH, 2292DSTOPTS x2, 2292RTHDR) and the three standard cases in the extension-header walk loop (DSTOPTS, ROUTING, default). AH retains an inline bounds check because its length formula differs ((ptr[1]+2)<<2). The walk loop also gets a pre-read bounds check at the top to validate ptr before any case accesses ptr[0] or ptr[1]. When the walk loop detects a corrupted header, return from the function instead of continuing to process later socket options.

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

The underlying weakness: Out-of-bounds Read

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

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.

More Out-of-bounds Read vulnerabilities (CWE-125)

Timeline

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

References

Recent Out-of-bounds Read vulnerabilities

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