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

CVE-2026-9539 is fixed in 2 products on 1 platform, first by libslirp0 4.9.1-1ubuntu1.1, released June 23, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-9539
- Priority: Routine
- CVSS: 6.5 (Moderate)
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 23, 2026
- Weakness: Out-of-bounds Read
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-9539

## 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).

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libslirp Debian 13.5 (trixie) | 4.8.0-1+deb13u1 | [DEBIAN-CVE-2026-9539](https://patchblox.com/security/data/fix/linux/debian-cve-2026-9539.md) | Jun 24, 2026 |
| Linux | libslirp Debian 14 | 4.9.2-1 | [DEBIAN-CVE-2026-9539](https://patchblox.com/security/data/fix/linux/debian-cve-2026-9539.md) | Jun 24, 2026 |
| Linux | libslirp opensuse-leap 16.0 | 4.8.0+2-160000.3.1 | [OPENSUSE-SU-2026:21216-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21216-1.md) | Jul 2, 2026 |
| Linux | libslirp sles 15.7 | 4.7.0+44-150500.4.3.1 | [SUSE-SU-2026:2931-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2931-1.md) | Jul 13, 2026 |
| Linux | libslirp0 Ubuntu 22.04.1 LTS (jammy) | 4.6.1-1ubuntu0.2 | [libslirp0 4.6.1-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libslirp0-4.6.1-1ubuntu0.2.md) | Jul 18, 2026 |
| Linux | libslirp0 Ubuntu 24.04.5 LTS (noble) | 4.7.0-1ubuntu3.1 | [libslirp0 4.7.0-1ubuntu3.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libslirp0-4.7.0-1ubuntu3.1.md) | Jul 18, 2026 |
| Linux | libslirp0 Ubuntu 26.04.1 LTS (resolute) | 4.9.1-1ubuntu1.1 | [libslirp0 4.9.1-1ubuntu1.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libslirp0-4.9.1-1ubuntu1.1.md) | Jun 23, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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