CVE-2026-80847
Dashboard / Vulnerabilities / CVE-2026-80847
Summary: tcp: clamp route advmss to TCP_MIN_MSS
Details: 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.
References: https://git.kernel.org/stable/c/31cf2349361902769dc323e4dbf4b449795ec288, https://git.kernel.org/stable/c/6b8c20bf61924dfc38fefb145c9f7406d73fae53, https://git.kernel.org/stable/c/870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1, https://git.kernel.org/stable/c/cfb44c6028e6f979720315e0772bbd0d4d33ed61, https://git.kernel.org/stable/c/eaf4af9bd6975c2eff8d48820937c83032d968dc, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80847.json, https://nvd.nist.gov/vuln/detail/CVE-2026-80847, https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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