Libsoup: libsoup: http/2 client crash in on_data_source_read_callback when settings initial_window_size shrinks during deferred body read
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.
- Published
- Sep 4, 2026
- Updated
- Sep 8, 2026
- EPSS
- 0.3% · 22th percentile
- CWE
- CWE-617
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Report tools
Action score
23
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.3%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · redhat
- 5.9
- NVD has not scored this yet; the score shown is the CNA’s.
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpAffected systems
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (redhat). Independent of NVD's CPE analysis and usually ahead of it.
Red Hat Red Hat Enterprise Linux 10
- all versionsaffected
Red Hat Red Hat Enterprise Linux 6
- all versionsunknown
Red Hat Red Hat Enterprise Linux 7
- all versionsunknown
Red Hat Red Hat Enterprise Linux 8
- all versionsunknown
Red Hat Red Hat Enterprise Linux 9
- all versionsunknown
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | libsoup3 | all versions | — |
| openSUSE:Leap 16.0 | libsoup | before 3.6.6-160000.4.1 | 3.6.6-160000.4.1 |
| openSUSE:Tumbleweed | libsoup | before 3.6.6-9.1 | 3.6.6-9.1 |
| SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | libsoup | before 3.0.4-150400.3.49.1 | 3.0.4-150400.3.49.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | libsoup | before 3.4.4-150600.3.53.1 | 3.4.4-150600.3.53.1 |
| SUSE:Linux Micro 6.0 | libsoup | before 3.4.2-18.1 | 3.4.2-18.1 |
| SUSE:Linux Micro 6.1 | libsoup | before 3.4.4-slfo.1.1_11.1 | 3.4.4-slfo.1.1_11.1 |
| SUSE:Linux Micro 6.2 | libsoup | before 3.6.6-160000.4.1 | 3.6.6-160000.4.1 |
Same product
red hat: all recordsOther highest-scoring records for the same primary product.
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- CVE-2025-4404Freeipa: idm: privilege escalation from host to domain admin in freeipa37Monitor
- CVE-2025-7493Freeipa: idm: privilege escalation from host to domain admin in freeipa36Monitor
- CVE-2025-49796Libxml: type confusion leads to denial of service (dos)36Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| azl3 libsoup 3.4.4-16 on Azure Linux 3.0 | Release Notes | Microsoft (MSRC) |
| azl3 libsoup 3.4.4-17 on Azure Linux 3.0 | Release Notes | Microsoft (MSRC) |
| opensuse:libsoup | 3.6.6-9.1 · openSUSE:Tumbleweed | Package registry (OSV) |
| suse:libsoup | 3.6.6-160000.4.1 · SUSE:Linux Micro 6.2 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-5271881 days apartGstreamer1-plugins-bad-free: gstreamer: denial of service via av1 tile_list_obu parser byte/bit confusion26Monitor
- CVE-2026-9114714 days apartCockpit: cockpit: denial of service in `cockpit-ws` due to url-root handling without a trailing slash23Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-617 · Reachable AssertionCVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
- access.redhat.com/security/cve/CVE-2026-85534
- bugzilla.redhat.com/show_bug.cgi?id=2528440
- gitlab.gnome.org/GNOME/libsoup/-/blob/master/libsoup/http2/soup-client-message-io-http2.c
- gitlab.gnome.org/GNOME/libsoup/-/work_items/551
Vendor advisories and official records. Exploit/PoC links are deliberately left out.