CVE-2026-72502 in Linux
Resumen
por MITRE • 2026-08-15
In the Linux kernel, the following vulnerability has been resolved:
tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)
When MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535). This is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.
However, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel. If a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will be mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer dereference because local TCP packets do not use frag_list.
Fix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from ip6_default_advmss() when MTU is large.
Also update the stale comment in ip6_default_advmss() which suggested that IPV6_MAXPLEN is returned to mean "any MSS".
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