tcp: clamp route advmss to TCP_MIN_MSS

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Summary

CVECVE-2026-80847
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-04 16:18:13 UTC
Updated2026-09-11 10:16:51 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: tcp: clamp route advmss to TCP_MIN_MSS tcp_select_initial_window() assumes that callers never pass an MSS smaller than 1, but route-derived advmss values can violate that assumption. A too-small explicit RTAX_ADVMSS is one way to get there, but it is not the only one. The same divide-by-zero can also be reached through the "default advmss" path when RTAX_ADVMSS is left at 0 and the effective advmss is later driven down by route MTU and min_adv_mss. Introduce a tcp_dst_advmss() helper that clamps route advmss to TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that derive advmss from dst metrics. This keeps the effective MSS from dropping to zero before tcp_select_initial_window() rounds the receive window.

Risk And Classification

EPSS: 0.001680000 probability, percentile 0.063710000 (date 2026-09-13)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 cfb44c6028e6f979720315e0772bbd0d4d33ed61 git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 6b8c20bf61924dfc38fefb145c9f7406d73fae53 git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 31cf2349361902769dc323e4dbf4b449795ec288 git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 git Not specified
CNA Linux Linux affected 2.6.12 Not specified
CNA Linux Linux unaffected 2.6.12 semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.13 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2.3 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/31cf2349361902769dc323e4dbf4b449795ec288 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6b8c20bf61924dfc38fefb145c9f7406d73fae53 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cfb44c6028e6f979720315e0772bbd0d4d33ed61 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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