PT-2025-37966 · Linux+1 · Linux Kernel+1

Mark Rutland · Published 2025-08-12 · Updated 2025-09-16 · CVE-2025-39821

Positive Technologies (AI Summary)

CVSS v3.1

7.8

High

Base vector

AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Name of the Vulnerable Software and Affected Versions Linux kernel (affected versions not specified)

Description The Linux kernel contains a flaw where calling pmu->start()/stop() on perf events in PERF EVENT STATE OFF can lead to undefined behavior. This occurs when event->hw.idx is at -1, and PMU drivers attempt to use this negative index as a shift exponent in bitwise operations, resulting in UBSAN shift-out-of-bounds reports. The issue arises from a logical flaw in how event groups handle throttling when some members are intentionally disabled. The throttling mechanism attempts to start/stop events that are not actively scheduled on the hardware.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Exploit

Out of bounds Read

Memory Corruption

Improper Initialization

Weakness Enumeration

CWE-125

CWE-787

CWE-665

CWE-1335

Related Identifiers

BDU:2026-03308

CVE-2025-39821

Affected Products

Astra Linux

Linux Kernel

References · 17

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39821.json · Exploit
• https://git.kernel.org/stable/c/d689135aa9c5e4e0eab5a92bbe35dab0c8d6677f · Patch
• https://ubuntu.com/security/CVE-2025-39821 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2025-39821 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2025-39821 · Vendor Advisory
• https://security-tracker.debian.org/tracker/CVE-2025-39821 · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2025-39821 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2025-39821 · Security Note
• https://bdu.fstec.ru/vul/2026-03308 · Security Note
• https://cve.org/CVERecord?id=CVE-2025-39821 · Security Note
• https://git.kernel.org/stable/c/b64fdd422a85025b5e91ead794db9d3ef970e369 · Patch
• https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git · Note
• https://lore.kernel.org/linux-cve-announce/2025091616-CVE-2025-39821-3812@gregkh · Note
• https://access.redhat.com/security/cve/cve-2025-39821 · Note
• https://git.kernel.org/linus/b64fdd422a85025b5e91ead794db9d3ef970e369 · Note