---
cve: "CVE-2026-23127"
severity: "LOW"
cvss: 3.1
epss: "11%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-02-14 15:16:07"
tags: [cve, security, low]
source: tsecurity.de CVE-Dossier
exported: "2026-09-06T10:56:54+02:00"
---

# CVE-2026-23127

> 3.1 LOW

## Beschreibung

In the Linux kernel, the following vulnerability has been resolved:

perf: Fix refcount warning on event->mmap_count increment

When calling refcount_inc(&event->mmap_count) inside perf_mmap_rb(), the
following warning is triggered:

        refcount_t: addition on 0; use-after-free.
        WARNING: lib/refcount.c:25

PoC:

    struct perf_event_attr attr = {0};
    int fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
    mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    int victim = syscall(__NR_perf_event_open, &attr, 0, -1, fd,
                         PERF_FLAG_FD_OUTPUT);
    mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_SHARED, victim, 0);

This occurs when creating a group member event with the flag
PERF_FLAG_FD_OUTPUT. The group leader should be mmap-ed and then mmap-ing
the event triggers the warning.

Since the event has copied the output_event in perf_event_set_output(),
event->rb is set. As a result, perf_mmap_rb() calls
refcount_inc(&event->mmap_count) when event->mmap_count = 0.

Disallow the case when event->mmap_count = 0. This also prevents two
events from updating the same user_page.

## Patch verfügbar (OSV)

- Kernel ≥ 6.18.8

## Referenzen

- <https://git.kernel.org/stable/c/23c0e4bd93d0b250775162faf456470485ac9fc7>
- <https://git.kernel.org/stable/c/d06bf78e55d5159c1b00072e606ab924ffbbad35>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-23127) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_