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CVE-2026-63920

ipv6: validate extension header length before copying to cmsg

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: partial

Summary

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: partial

  3. Record last updated

Affected versions

  • Linux Linux

    From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 81394827dfb72772c50d0ae3bdfa094428a5d76d; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 931b4a1f13408c2507719890f78f7227c34a0282; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 08464413e628803bd10cb1df68d0138665f2f885; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in a29768d56eb3798c052ad3281b05596e695a17af; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 0d330eff318c0f44d4fb0ad2c2aef38f87f24c90; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in a35daeabb433686234b010ebf7b53778dbd6c9b8; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in eb18a1b1644e4cad978df2131e2bb9a2e6886992; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in dd433671fef381fdaf7b530c631e6b782d66e224

  • Linux Linux

    2.6.12

  • KernelLinux

    From 2.6.12 · fixed in 5.10.259; From 5.11.0 · fixed in 5.15.210; From 5.16.0 · fixed in 6.1.176; From 6.2.0 · fixed in 6.6.143; From 6.7.0 · fixed in 6.12.93; From 6.13.0 · fixed in 6.18.35; From 6.19.0 · fixed in 7.0.12

References 8

git.kernel.org