# CVE-2026-102557: libsoup heap corruption in WebSocket message reassembly

Source: https://junglewise.ai/threats/cve-2026-102557-a-flaw-was-found-in-libsoup-when-reassembling-fragmented  
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-2026-102557 · Severity: high · CVSS 8.6 · Published 2026-09-29

libsoup is a networking library used by applications to communicate over the web. When handling WebSocket messages from remote peers, libsoup fails to properly limit the size of reassembled messages, allowing an attacker to send specially crafted fragments that trigger heap corruption or crash the application. This affects any application using libsoup's WebSocket functionality with untrusted network peers.

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

## Quick answers

**Is CVE-2026-102557 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102557 being exploited in the wild.

**How severe is CVE-2026-102557?** 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-2026-102557?** 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-2026-102557 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-102557?** 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 is an out-of-bounds read (CWE-125) in libsoup's WebSocket message reassembly logic. When fragmented WebSocket messages are reassembled into a GByteArray, the implementation does not adequately validate total message size against buffer type limits, causing integer truncation. A remote, unauthenticated peer can send crafted message fragments over the network to trigger heap corruption, information disclosure, or denial of service without requiring user interaction or prior authentication.

## 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-2026-102557](https://access.redhat.com/security/cve/CVE-2026-102557)

## 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 heap buffer overflow in WebSocket handling](https://junglewise.ai/threats/cve-2026-102558-a-flaw-was-found-in-libsoup-when-max-incoming-payload-size-is)
- [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 type confusion in WebSocket Pong signal](https://junglewise.ai/threats/cve-2026-102556-a-flaw-was-found-in-libsoup-when-handling-an-incoming-websocket)