# CVE-2026-102558: libsoup heap buffer overflow in WebSocket handling

Source: https://junglewise.ai/threats/cve-2026-102558-a-flaw-was-found-in-libsoup-when-max-incoming-payload-size-is  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-29  
License: CC BY 4.0 with a link back

CVE-2026-102558 · Severity: high · CVSS 8.6 · Published 2026-09-29

libsoup is a widely-used HTTP and WebSocket library for applications on Linux systems. When configured with unlimited incoming payload size, a remote WebSocket peer can trigger a heap buffer overflow that leads to memory corruption, denial of service, or potential information disclosure. Applications using the default secure configuration with a finite payload limit are at reduced risk, but custom configurations that disable this limit remain vulnerable.

Technologies: [Gnome Libsoup](https://junglewise.ai/threats/technologies/libsoup). Vendors: [Gnome](https://junglewise.ai/threats/vendors/gnome).

## Quick answers

**Is CVE-2026-102558 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102558 being exploited in the wild.

**How severe is CVE-2026-102558?** High severity, with a CVSS score of 8.6, published 29 September 2026.

**Which products and versions are affected?** GNOME libsoup.

**Is there a fix for CVE-2026-102558?** 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-2026-102558 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-102558?** Check whether you run Gnome Libsoup. 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 SoupWebsocketConnection when max-incoming-payload-size is set to 0 (unlimited). An attacker-controlled WebSocket frame length can cause the incoming GByteArray to grow until integer wrapping occurs, resulting in a heap buffer overflow during frame data reading. This requires network access to a WebSocket endpoint and affects both memory safety and availability; the attack is unauthenticated and requires no user interaction.

## Affected products

- GNOME libsoup

## Timeline

- 2026-09-29: 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-2026-102558](https://access.redhat.com/security/cve/CVE-2026-102558)

## Related threats

- [libsoup HTTP request smuggling via undrained Expect: 100-continue body](https://junglewise.ai/threats/cve-2026-103399-a-flaw-was-found-in-soupserver-libsoup-when-an-http-1-x-client)
- [libsoup heap buffer overflow in permessage-deflate WebSocket extension](https://junglewise.ai/threats/cve-2026-102560-a-flaw-was-found-in-libsoup-when-the-permessage-deflate)
- [libsoup out-of-bounds read in data-URI base64 decoding](https://junglewise.ai/threats/cve-2026-102555-a-flaw-was-found-in-libsoup-the-soup-uri-decode-data-uri)
- [libsoup heap corruption in WebSocket message reassembly](https://junglewise.ai/threats/cve-2026-102557-a-flaw-was-found-in-libsoup-when-reassembling-fragmented)
- [libsoup type confusion in WebSocket Pong signal](https://junglewise.ai/threats/cve-2026-102556-a-flaw-was-found-in-libsoup-when-handling-an-incoming-websocket)