CVE-2026-80847: Linux

EPSS: 0.2% chance of exploitation in the next 30 days.

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 products

• Linux Linux: from 2.6.12, before 6.12.111 (fixed in 6.12.111); from 6.13, before 6.18.51 (fixed in 6.18.51); from 6.19, before 7.1.13 (fixed in 7.1.13); from 7.2, before 7.2.3 (fixed in 7.2.3)

Published 2026-09-04. Last modified 2026-09-21.