Bug 2543224 (CVE-2026-102555)

Summary:	CVE-2026-102555 libsoup: libsoup: Heap buffer overflow via uninitialized length in data-URI base64 decoding
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
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Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in libsoup. The soup_uri_decode_data_uri() function incorrectly treated base64 data-URI payloads as NUL-terminated strings when calling g_base64_decode_inplace(). If the percent-decoded payload contained embedded NUL bytes, the decoded length could remain uninitialized and be used as the size of the returned GBytes. This can lead to an out-of-bounds read or application crash when processing a crafted data URI.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2543268, 2543269, 2543270
Bug Blocks:

Description OSIDB Bzimport 2026-09-29 14:47:10 UTC

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