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ipv6: validate extension header length before copying to cmsg (Linux Linux)

CVE-2026-63920
HIGH 7.1

At a glance

Source
NVD
EPSS
EPSS 0.17 % · percentile 7 ()
State
PUBLISHED
Published
Updated
Assigner
Linux
NVD status
Analyzed

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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.

Weaknesses (CWE)

References

Scores

VersionScoreVectorScored by
CVSS 3.1HIGH 7.1CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:HLinux
CVSS 3.1HIGH 7.1CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:HNVD · 416baaa9-dc9f-4396-8d5f-8c081fb06d67 (Secondary)

European references

CERT-FR advisories

Affected configurations (NVD CPE)

Affected products

ProductVersions
Linux · Linuxaffected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 81394827dfb72772c50d0ae3bdfa094428a5d76d ; affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 931b4a1f13408c2507719890f78f7227c34a0282 ; affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 08464413e628803bd10cb1df68d0138665f2f885 ; affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a29768d56eb3798c052ad3281b05596e695a17af ; affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0d330eff318c0f44d4fb0ad2c2aef38f87f24c90 ; affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a35daeabb433686234b010ebf7b53778dbd6c9b8
Linux · Linuxaffected 2.6.12 ; unaffected 0 < 2.6.12 ; unaffected 5.10.259 ≤ 5.10.* ; unaffected 5.15.210 ≤ 5.15.* ; unaffected 6.1.176 ≤ 6.1.* ; unaffected 6.6.143 ≤ 6.6.*

Sources

SourceLicence
CVE List (CVEProject cvelistV5)CVE Program Terms of Use
EPSS (FIRST.org)FIRST — attribution requested
ENISA EUVDENISA — reproduction authorised, source acknowledged
CERT-FR (ANSSI)Licence Ouverte / Etalab 2.0
NVD (NIST) via fkie-cad/nvd-json-data-feedsPublic domain — this product uses data from the NVD API but is not endorsed or certified by the NVD