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Fencer Vulns
medium 6.5

CVE-2026-9539 json

libslirp TCP URG OOB Read Information Leak

published 2026-06-24 4 mo ago modified 2026-10-25 14 d ago also EUVD-2026-38654

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits
0
none known

Summary

An out-of-bounds heap read and integer underflow in the TCP urgent data handling (sosendoob) in freedesktop.org libslirp version before v4.9.2 on hypervisor host environments (e.g., QEMU) allows a privileged guest VM attacker (root or CAP_NET_RAW) to leak gigabytes of sensitive host-process heap memory via sending crafted TCP segments with manipulated URG flags and urgent pointers (ti_urp).

Patch / fix

  • freedesktop.org libslirp 4.9.2
  • libslirp Debian 13 4.8.0-1+deb13u1
  • libslirp Debian 14 4.9.2-1

debian advisories DEBIAN-CVE-2026-9539

  • libslirp Ubuntu 22.04 LTS 4.6.1-1ubuntu0.2
  • libslirp Ubuntu 24.04 LTS 4.7.0-1ubuntu3.1
  • libslirp Ubuntu 26.04 LTS 4.9.1-1ubuntu1.1

ubuntu advisories UBUNTU-CVE-2026-9539

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libslirp SLE Module for Basesystem 15 SP7, SLE Micro 5.5 4.7.0+44-150500.4.3.1
  • libslirp SLE Micro 5.4, SLE Micro 5.3 4.7.0+44-150300.18.1
  • libslirp Linux Micro 6.0 4.7.0+44-5.1
  • libslirp Linux Micro 6.1 4.8.0+2-slfo.1.1_2.1

suse advisories SUSE-SU-2026:2931-1SUSE-SU-2026:2886-1SUSE-SU-2026:22514-1SUSE-SU-2026:22452-1

  • libslirp openSUSE Leap 16.0 4.8.0+2-160000.3.1
  • libslirp openSUSE Tumbleweed 4.9.3+4-1.1

opensuse advisories openSUSE-SU-2026:21216-1openSUSE-SU-2026:11134-1

  • libslirp Azure Linux 3.0 4.9.3-1

azure linux advisories AZL-90912

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-9539 updated cvss 6.5

libslirp: libslirp: Information Disclosure via TCP Urgent Data Handling

  • Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gitlab.freedesktop.org https://gitlab.freedesktop.org/slirp/libslirp/-/work_items/93 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

Affected products

  • freedesktop.org libslirp

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.