net: ipv6: Fix UDP length overflow with PMTU discover and big MTU
Summary
| CVE | CVE-2026-97984 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-25 11:17:26 UTC |
| Updated | 2026-09-25 11:17:26 UTC |
| Description | In the Linux kernel, the following vulnerability has been resolved: net: ipv6: Fix UDP length overflow with PMTU discover and big MTU This commit bounds cork->base.fragsize to IP6_MAX_MTU for UDP sockets to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IPV6_MTU_DISCOVER is set to IPV6_PMTUDISC_DO or IPV6_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU. Steps to reproduce (included in the new selftest): 1. Set device MTU bigger than IP6_MAX_MTU. cork->base.fragsize will be set to that MTU in ip6_setup_cork. 2. Set IPV6_MTU_DISCOVER to IPV6_PMTUDISC_PROBE or IPV6_PMTUDISC_DO. It lets maxnonfragsize be set to device MTU (cork->fragsize) in __ip6_append_data, rather than to IP6_MAX_MTU. 3. Send 65528 bytes of payload (+8 bytes of UDP header, +40 bytes of IPv6 header). Device MTU allows it (it's only one byte bigger than IP6_MAX_MTU, and the device MTU is bigger than that). 4. The UDP length in the built packet is 65536, which overflows the 16-bit length field and triggers the WARN in udp_set_len_short. To avoid breaking sending UDP jumbograms over raw IPv6 sockets, limit the change to UDP sockets only. The original overflow bug with IPv6 and IPV6_PMTUDISC_DO seems to predate git history (verified reproduction on 2.6.21), was fixed later, and then reappeared in commit 427faee167bc ("net: ipv6: introduce ip6_dst_mtu_maybe_forward"), which is chosen as the Fixes tag here. The overflow with IPV6_PMTUDISC_PROBE reproduces since its introduction in commit 628a5c561890 ("[INET]: Add IP(V6)_PMTUDISC_RPOBE"). |
Risk And Classification
EPSS: 0.001680000 probability, percentile 0.053850000 (date 2026-09-27)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 427faee167bce4ccb0b22f6815a9ac509e31d4c3 1d56a00ec91f2885c64ea5b8cea18cb746b91bbb git | Not specified |
| CNA | Linux | Linux | affected 427faee167bce4ccb0b22f6815a9ac509e31d4c3 ce66352d3eb21825410af8b91db7cc4bb8e22c98 git | Not specified |
| CNA | Linux | Linux | affected 427faee167bce4ccb0b22f6815a9ac509e31d4c3 e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc git | Not specified |
| CNA | Linux | Linux | affected 427faee167bce4ccb0b22f6815a9ac509e31d4c3 0ae10b6be49b425827659b23bcce498f80eb7182 git | Not specified |
| CNA | Linux | Linux | affected 5.15 | Not specified |
| CNA | Linux | Linux | unaffected 5.15 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.12.111 6.12.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.53 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2.7 7.2.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.3-rc3 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/ce66352d3eb21825410af8b91db7cc4bb8e22c98 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/1d56a00ec91f2885c64ea5b8cea18cb746b91bbb | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/0ae10b6be49b425827659b23bcce498f80eb7182 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.