CVE-2026-72502
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk50th percentile - higher than 50% of all known CVEs
Summary
In the Linux kernel's TCP for IPv6, the ip6_default_advmss() function can return IPV6_MAXPLEN (65535), which is interpreted as mss_clamp, allowing MSS to reach 65535. However, 0xFFFF is also used as a magic value GSO_BY_FRAGS, which can lead to a NULL pointer dereference during TCP packet segmentation.
Risk Assessment
Risk of system crash (kernel panic) or potential exploitation for privilege escalation due to NULL pointer dereference.
Recommendation
Apply the Linux kernel update containing the fix for CVE-2026-72502.
Original NVD description (English source)
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".