# CVE-2026-120830: libslirp out-of-bounds heap read in icmp_forward_error()

Source: https://junglewise.ai/threats/cve-2026-120830-a-flaw-was-found-in-libslirp-in-icmp-forward-error-when-building  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-03. Updated: 2026-11-03  
License: CC BY 4.0 with a link back

CVE-2026-120830 · Severity: high · CVSS 7.4 · Published 2026-11-03

libslirp is a user-mode TCP/IP network emulation library used in virtual machines and containers to provide network connectivity. A flaw in its ICMP error handling allows a guest or container to send a malformed packet that triggers an out-of-bounds memory read, leaking sensitive host memory back to the guest—exposing data that should remain private.

Vendors: [Freedesktop](https://junglewise.ai/threats/vendors/freedesktop).

## Quick answers

**Is CVE-2026-120830 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-120830 being exploited in the wild.

**How severe is CVE-2026-120830?** High severity, with a CVSS score of 7.4, published 3 November 2026.

**Which products and versions are affected?** freedesktop libslirp.

**Is there a fix for CVE-2026-120830?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-120830 attacked?** It is attacked from the adjacent network, in a software library.

**Am I affected by CVE-2026-120830?** Check whether you run Freedesktop Libslirp. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the icmp_forward_error() function, which builds ICMP error responses without clamping the quoted original IPv4 packet length to the actual buffer size. A truncated or malformed packet causes an out-of-bounds heap read from the host process memory. Attack requires network-adjacent access (a guest or container with network capability), no authentication or user interaction.

## Affected products

- freedesktop libslirp

## Timeline

- 2026-11-03: disclosed

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-120830](https://access.redhat.com/security/cve/CVE-2026-120830)