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libsoup CVE-2026-85534

| EUVDEUVD-2026-70997 MEDIUM
Reachable Assertion (CWE-617)
2026-09-04 redhat GHSA-qm5f-xr9c-mm27
5.9
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
5.9 MEDIUM

Network-reachable via malicious server (AV:N), but requires precise timing of SETTINGS shrink against non-pollable stream buffer (AC:H); impact is process abort only (A:H, C:N, I:N).

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
8.1 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Red Hat
5.9 MEDIUM
qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

3
Metadata Corrected
Sep 04, 2026 - 11:40 vuln.today
tag: Information Disclosure removed
Analysis Generated
Sep 04, 2026 - 10:51 vuln.today
CVE Published
Sep 04, 2026 - 10:19 cve.org
MEDIUM 5.9

DescriptionCVE.org

A flaw was found in libsoup. When a client sends an HTTP/2 request body from a non-pollable input stream, the library can buffer more data than the current flow-control window later allows. A malicious HTTP/2 server can shrink SETTINGS_INITIAL_WINDOW_SIZE while that buffered read is still in progress. The client then copies the full buffer into a smaller DATA callback without a runtime bounds check, which can abort the process or fail the HTTP/2 session.

AnalysisAI

HTTP/2 flow-control window mismanagement in libsoup (GNOME's HTTP client/server library) allows a malicious HTTP/2 server to abort a connecting client process or crash its HTTP/2 session. When the client sends a request body sourced from a non-pollable GInputStream, libsoup buffers the data before transmission; a server that then shrinks SETTINGS_INITIAL_WINDOW_SIZE causes the client to copy the full pre-buffered payload into a now-undersized DATA callback without a runtime bounds check, triggering a reachable assertion abort (CWE-617). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires the following specific conditions to align simultaneously: (1) the client must be communicating over HTTP/2, not HTTP/1.x; (2) the HTTP/2 request must include a body provided via a non-pollable GInputStream - a specific GLib I/O stream type that cannot be monitored by polling - causing libsoup to buffer the payload; (3) the client must connect to an attacker-controlled or attacker-influenced HTTP/2 server capable of issuing a SETTINGS frame with a reduced SETTINGS_INITIAL_WINDOW_SIZE; and (4) the server must time this SETTINGS frame while the buffered read is still unresolved. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 5.9 (AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H) accurately captures the constrained exploitation surface: triggering the race requires the server to shrink SETTINGS_INITIAL_WINDOW_SIZE at the precise moment between buffer fill and DATA callback execution, making reliable exploitation non-trivial. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation No vendor-released patch with an exact fix version has been identified at time of analysis. … Detailed patch versions, workarounds, and compensating controls in full report.

Threat intelligence, references, and detailed analysis are available after sign-in.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise Micro 5.3 Not-Affected
SUSE Linux Enterprise Micro 5.4 Not-Affected
SUSE Linux Enterprise Micro 5.5 Not-Affected

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CVE-2026-85534 vulnerability details – vuln.today

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