CVE-2026-9539 libslirp TCP URG OOB Read Information Leak

Medium 6.5 Published 24 Jun 2026 Updated 24 Jun 2026

A privileged guest VM attacker can leak host heap memory via crafted TCP segments in libslirp, impacting hypervisor hosts like QEMU.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-9539?

CVE-2026-9539 is a medium-severity vulnerability in freedesktop.org libslirp, published on 24 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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).

Weakness: CWE-125

Which versions are affected by CVE-2026-9539?

Linux distribution packages (8)

`libslirp` SUSE:Linux Enterprise Micro 5.3	All versions	`4.7.0+44-150300.18.1`
`libslirp` SUSE:Linux Enterprise Micro 5.4	All versions	`4.7.0+44-150300.18.1`
`libslirp` SUSE:Linux Enterprise Micro 5.5	All versions	`4.7.0+44-150500.4.3.1`
`libslirp` SUSE:Linux Enterprise Module for Basesystem 15 SP7	All versions	`4.7.0+44-150500.4.3.1`
`libslirp` SUSE:Linux Micro 6.0	All versions	`4.7.0+44-5.1`
`libslirp` SUSE:Linux Micro 6.1	All versions	`4.8.0+2-slfo.1.1_2.1`
`libslirp` openSUSE:Leap 16.0	All versions	`4.8.0+2-160000.3.1`
`libslirp` openSUSE:Tumbleweed	All versions	`4.9.3+4-1.1`

How do I fix CVE-2026-9539?

Upgrade to a fixed version.

Is CVE-2026-9539 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-9539 exists.

Public exploit code: 1 proofs of concept on GitHub.

Sources

Also known as AZL-90912, BELL-CVE-2026-9539, DEBIAN-CVE-2026-9539, GHSA-4243-hp56-4m7f, MGASA-2026-0306, SUSE-SU-2026:22452-1 and 7 more.