VulnerabilityPublished 18 Oct 2026

CVE-2026-98551: Linux kernel · perf/core: Fill branch entries with a single assignment

Source GCVE Database

Authoritative record:CVE-2026-98551· Medium

Not known to be exploited : upgrade to c7de8521947a521b766979ff5c09f66fe905a5bd or 24b620729e53d978b3e425f55bc66efd3bab1f59 when convenient.

Data as of 26 Oct 2026, 12:55 UTC

Severity

Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in c7de8521947a521b766979ff5c09f66fe905a5bd, 24b620729e53d978b3e425f55bc66efd3bab1f59

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-r5w5-qjwh-6pq3

What to do

Upgrade Linux kernel to c7de8521947a521b766979ff5c09f66fe905a5bd or 24b620729e53d978b3e425f55bc66efd3bab1f59.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ b190bc4ac9e6d9763b61654c5a0c085ff77d7a09, < c7de8521947a521b766979ff5c09f66fe905a5bd	Fixed in c7de8521947a521b766979ff5c09f66fe905a5bd
LinuxLinux	Affected ≥ b190bc4ac9e6d9763b61654c5a0c085ff77d7a09, < 24b620729e53d978b3e425f55bc66efd3bab1f59	Fixed in 24b620729e53d978b3e425f55bc66efd3bab1f59
LinuxLinux	Affected =6.1	Fixed in–

AI-suggested

A fix has been implemented in the Linux kernel that assigns the entire perf_branch_entry struct at once, ensuring all fields are properly initialized. Users should update to the kernel version containing this fix. Since this is a kernel-level issue, applying the official kernel update is the recommended remediation.

Description

A vulnerability in the Linux kernel's perf subsystem related to branch entry handling has been resolved. The issue involved improper clearing of bitfields in the perf_branch_entry struct, leading to uninitialized data being exposed in certain ARM64 configurations. The fix assigns the entire entry at once to ensure all fields are properly initialized. This vulnerability affects the ARM64 architecture and does not impact x86. No CVSS score is available for this issue.

Impact

Uninitialized memory data from the perf branch stack could be exposed to userspace on ARM64 Linux systems, potentially leaking sensitive kernel memory contents. The vulnerability does not affect x86 architectures and is limited to the perf subsystem's branch stack handling. There is no indication of active exploitation in the wild.

Summary

The vulnerability in the Linux kernel perf subsystem was due to perf_clear_branch_entry_bitfields() clearing bitfields of struct perf_branch_entry individually but leaving some fields (new_type and priv) uninitialized. These fields were added later and not properly cleared, causing uninitialized memory data to be exposed in userspace on ARM64 systems when perf branch stack records were processed. The patch replaces per-field clearing with a single assignment of the entire struct, ensuring all fields are zeroed and consistent. The function perf_clear_branch_entry_bitfields() was removed as it had no callers left. This issue does not affect x86 architectures and is specific to ARM64 due to how the per-CPU branch stack is allocated and handled.

References

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