Is there a public exploit for CVE-2026-99191?

No public exploit for CVE-2026-99191 was found in Exploit-DB, Metasploit, Nuclei templates or public proof-of-concept repositories. That is an absence of evidence rather than proof that none exists.

— Unscored

In the Linux kernel, the following vulnerability has been resolved: calipso: keep BIG TCP payloadlen in calipsoskbuffsetattr()…

CVE-2026-99191

In the Linux kernel, the following vulnerability has been resolved: calipso: keep BIG TCP payloadlen in calipsoskbuffsetattr() calipsoskbuffsetattr() adjusts payloadlen by the length of the option it inserts or resizes: payload = ntohs(ip6hdr->payloadlen); ip6hdr->payloadlen = htons(payload + lendelta); GRO can build BIG TCP packets larger than IPV6MAXPLEN, and stores payloadlen == 0 for them; ipv6payloadlen() then falls back to skb->len. For such a packet forwarded to a destination mapped to CALIPSO, the code above writes lendelta (or 65536 + lendelta when shrinking) into payloadlen, and ipv6payloadlen() no longer falls back to skb->len. nftables, conntrack and schcake rely on it. The same arithmetic also wraps when a packet grows past IPV6MAXPLEN, and a BIG TCP packet that shrinks below IPV6MAXPLEN should get its real length back. Set payloadlen from the skb length with ipv6setpayloadlen(), which stores 0 above IPV6MAXPLEN and the real length otherwise, as ipv6grocomplete() does. The network header was just reset to skb->data, so skb->len - sizeof(ip6hdr) is the payload length. Tested on one kernel (arm64, QEMU) with SELinux permissive, a minimal mdp-generated policy…

Assessment

CVSS: Not yet scored
Severity: Unscored
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 28 October 2026
Last updated: 30 October 2026
Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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