Bug 2543268

Summary: CVE-2026-102555 libsoup: libsoup: Heap buffer overflow via uninitialized length in data-URI base64 decoding [fedora-all]
Product: [Fedora] Fedora Reporter: Srikanth Balasubramanian <sbalasub>
Component: libsoupAssignee: Gwyn Ciesla <gwync>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: high Docs Contact:
Priority: high    
Version: rawhideCC: gwync, mclasen, rhughes, rstrode, tpopela
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["d57892d1-6024-47eb-aa0d-f8d0db1fa6a7"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On:    
Bug Blocks: 2543224    

Description Srikanth Balasubramanian 2026-09-29 15:58:00 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A heap buffer overflow condition was found in libsoup's soup_uri_decode_data_uri().

After percent-decoding a data URI payload marked ;base64, the code called g_base64_decode_inplace(), which measures input with strlen(). Percent-decoded content can contain embedded NUL bytes (for example data:;base64,A%00B), so the measured length was too short. g_base64_decode_inplace() returned without writing a valid output length; the uninitialized length was then stored as the size of the returned GBytes, allowing callers to read past the allocation.

Fixed upstream by decoding with g_base64_decode_step() using the real buffer length (commit e4f03226, libsoup 3.7.3).

References:
https://gitlab.gnome.org/GNOME/libsoup/-/work_items/554 (Bug 1)
https://gitlab.gnome.org/GNOME/libsoup/-/commit/e4f03226