# CVE-2026-12548: GNOME libsoup heap out-of-bounds read in multipart HTTP parsing

Source: https://junglewise.ai/threats/cve-2026-12548-gnome-libsoup-heap-out-of-bounds-read-in-multipart-http-parsing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-21. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-12548 · Severity: medium · CVSS 4.2 · Published 2026-07-21

libsoup is a popular networking library used by many Linux applications to handle web communications. A flaw was found in how it processes complex web messages containing multiple parts (multipart HTTP messages). If an application using this library receives a specially crafted, extremely large message, it could cause the application to crash or potentially allow an attacker to view sensitive information stored in the computer's memory.

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

## Quick answers

**Is CVE-2026-12548 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-12548 being exploited in the wild.

**How severe is CVE-2026-12548?** Medium severity, with a CVSS score of 4.2, published 21 July 2026.

**Which products and versions are affected?** Gnome Libsoup Red Hat Enterprise Linux 10 (affected).

**Is there a fix for CVE-2026-12548?** 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-2026-12548 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-12548?** Check whether you run Gnome Libsoup at an affected version. 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

A heap out-of-bounds read (CWE-125) exists in libsoup's multipart body parser due to an integer truncation vulnerability. In `soup_multipart_new_from_message()`, the length of a MIME part's header section is calculated as a 64-bit `ptrdiff_t`. When this value exceeds `INT_MAX` (approx. 2 GiB), it is truncated to a 32-bit signed `int` when passed to `soup_headers_parse()`, resulting in a negative value. This negative integer is subsequently cast to a large `size_t` when passed to `memchr()`, triggering a massive out-of-bounds read. An attacker can exploit this by sending a crafted multipart HTTP message to a libsoup-based client or server to cause a denial of service (crash) or potentially disclose heap memory contents.

## Affected products

- Red Hat libsoup3 Red Hat Enterprise Linux 10 (affected)
- GNOME libsoup 3.x versions prior to fix

## Timeline

- 2026-01-28: disclosed: Reported via YesWeHack program
- 2026-07-21: advisory: NVD and Red Hat published advisory details

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-12548](https://access.redhat.com/security/cve/CVE-2026-12548)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2489996](https://bugzilla.redhat.com/show_bug.cgi?id=2489996)
- [https://gitlab.gnome.org/GNOME/libsoup/-/work_items/512](https://gitlab.gnome.org/GNOME/libsoup/-/work_items/512)

## 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 heap corruption in WebSocket message reassembly](https://junglewise.ai/threats/cve-2026-102557-a-flaw-was-found-in-libsoup-when-reassembling-fragmented)