# CVE-2026-99234: tracing: Unregister field variable histograms when the command fails

CVE-2026-99234 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99234, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99234
- Priority: Routine
- CVSS: 3.4 (Low)
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Nov 2, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99234

## Description

In the Linux kernel, the following vulnerability has been resolved:  tracing: Unregister field variable histograms when the command fails  An action that names a field on another event needs that field as a variable, so create_field_var_hist() registers a second hist trigger on that event to provide it, and records it in target_hist_data->field_var_hists[].  If a later part of the same command fails, create_actions() returns an error and event_hist_trigger_parse() jumps to out_free. The write fails with -EINVAL and sched_switch gets no trigger, but:    # echo 'hist:keys=pid:ts0=common_timestamp.usecs' >> \       events/sched/sched_waking/trigger   # echo 'my_synth u64 lat; int a; int b' >> synthetic_events   # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\       onmatch(sched.sched_waking).my_synth($wakeup_lat,prio,nosuchfld)'\       >> events/sched/sched_switch/trigger   # cat events/sched/sched_waking/trigger   hist:keys=pid:vals=hitcount:ts0=common_timestamp.usecs:sort=hitcount:size=2048:clock=global [active]   hist:keys=pid:vals=hitcount:synthetic_prio=prio:sort=hitcount:size=2048 [active]  The second histogram is the one created for 'prio'. It is still active and still counting.  out_free reaches destroy_field_var_hists(), which frees the field_var_hists[] entries, but never unregister_field_var_hists(), which is what removes the triggers and runs only from event_hist_trigger_free(). The entry is freed and the trigger is left with nothing tracking it.  Unregister the field variable histograms in out_free as well, and record each one as soon as its trigger is registered rather than after the lookup that follows it, so no exit can leave a registered trigger untracked. The entry then belongs to field_var_hists[] and is released by destroy_field_var_hists(), so freeing it on that exit would be a double free.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-1 | [DEBIAN-CVE-2026-99234](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99234.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.14-1 | [DEBIAN-CVE-2026-99234](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99234.md) | Nov 3, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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