CVE-2026-80847

Summary

In 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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6b8c20bf61924dfc38fefb145c9f7406d73fae53affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 31cf2349361902769dc323e4dbf4b449795ec288affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1affected
LinuxLinux2.6.12affected
LinuxLinux0 < 2.6.12unaffected
LinuxLinux7.1.13 <= 7.1.*unaffected
LinuxLinux7.2.3 <= 7.2.*unaffected
LinuxLinux7.3-rc1 <= *unaffected

Weaknesses

References