CVE-2026-85534

MEDIUMPre-NVD 5.95.9—
EchelonGraph scoreHIGH confidence

Score 5.9 from GitHub Security Advisory published 2026-09-04. a secondary CVSS source baseline 5.9; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
5.9
EG Score
5.9(high)
EG Risk
27(Track)
EG Risk 27/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity59% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
25%
KEV
Not listed

Published

September 4, 2026

Last Modified

September 8, 2026

Advisory Details (4)

Auto-updated Sep 4, 2026
🔬 Proof of concept available. Patch available. Sources: redhat.
generic🟡 PoC Available

(#YWH-PGM9867-273) Heap Overflow on SoupSession through on_data_source_read_callback() in libsoup/http2/soup-client-message-io-http2.c via SETTINGS frame with INITIAL_WINDOW_SIZE Manipulation (#551) · Issues · GNOME / libsoup · GitLab

https://gitlab.gnome.org/GNOME/libsoup/-/work_items/551
generic

Client Challenge

https://gitlab.gnome.org/GNOME/libsoup/-/blob/master/libsoup/http2/soup-client-message-io-http2.c
redhat

2528440 – (CVE-2026-85534) CVE-2026-85534 libsoup: libsoup: HTTP/2 client crash in on_data_source_read_callback when SETTINGS INITIAL_WINDOW_SIZE shrinks during deferred body read

https://bugzilla.redhat.com/show_bug.cgi?id=2528440
redhat Patch Available

CVE-2026-85534 - Red Hat Customer Portal

Affected: Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to a

https://access.redhat.com/security/cve/CVE-2026-85534

Vendor Advisories for CVE-2026-85534(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(5 across 3 ecosystems)
Debian:12(2)
PackageVulnerable rangeFixed inDependents
libsoup2.42.74.3-1 ... 2.74.3-9 (16 versions)——
libsoup33.2.2-2 ... 3.6.6-1 (35 versions)——
Debian:13(2)
PackageVulnerable rangeFixed inDependents
libsoup2.42.74.3-10.1, 2.74.3-11——
libsoup33.6.5-3 ... 3.6.6-1 (8 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
libsoup33.6.5-3 ... 3.6.6-1 (8 versions)——

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 24× in last 7d / 48× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-18 19:28 UTCEPSS rescore
  2. 2026-09-18 16:24 UTCEG score recompute
  3. 2026-09-18 16:24 UTCVendor advisory
  4. 2026-09-18 16:24 UTCGHSA enrichment
  5. 2026-09-17 19:32 UTCEPSS rescore
  6. 2026-09-17 14:17 UTCEG score recompute
  7. 2026-09-17 14:17 UTCVendor advisory
  8. 2026-09-17 14:17 UTCGHSA enrichment
  9. 2026-09-16 14:09 UTCEPSS rescore
  10. 2026-09-16 12:06 UTCEG score recompute
  11. 2026-09-16 12:06 UTCVendor advisory
  12. 2026-09-16 12:06 UTCGHSA enrichment
  13. 2026-09-16 05:15 UTCEPSS rescore
  14. 2026-09-15 09:58 UTCEG score recompute
  15. 2026-09-15 09:58 UTCVendor advisory
  16. 2026-09-15 09:58 UTCGHSA enrichment
  17. 2026-09-15 03:12 UTCEPSS rescore
  18. 2026-09-15 03:12 UTCEPSS rescore
  19. 2026-09-14 07:51 UTCEG score recompute
  20. 2026-09-14 07:51 UTCVendor advisory
  21. 2026-09-14 07:51 UTCGHSA enrichment
  22. 2026-09-13 05:44 UTCEG score recompute
  23. 2026-09-13 05:44 UTCVendor advisory
  24. 2026-09-13 05:44 UTCGHSA enrichment
  25. 2026-09-12 03:37 UTCEG score recompute
Show 23 more
  1. 2026-09-12 03:37 UTCVendor advisory
  2. 2026-09-12 03:37 UTCGHSA enrichment
  3. 2026-09-11 14:53 UTCEPSS rescore
  4. 2026-09-11 14:53 UTCEPSS rescore
  5. 2026-09-11 01:30 UTCEG score recompute
  6. 2026-09-11 01:30 UTCGHSA enrichment
  7. 2026-09-09 23:23 UTCEG score recompute
  8. 2026-09-09 23:23 UTCGHSA enrichment
  9. 2026-09-08 22:01 UTCEPSS rescore
  10. 2026-09-08 19:57 UTCGHSA enrichment
  11. 2026-09-07 22:41 UTCEG score recompute
  12. 2026-09-07 22:41 UTCGHSA enrichment
  13. 2026-09-06 20:33 UTCEG score recompute
  14. 2026-09-06 20:33 UTCGHSA enrichment
  15. 2026-09-06 13:48 UTCEPSS rescore
  16. 2026-09-05 18:26 UTCEG score recompute
  17. 2026-09-05 18:26 UTCGHSA enrichment
  18. 2026-09-05 15:31 UTCEPSS rescore
  19. 2026-09-04 16:20 UTCEG score recompute
  20. 2026-09-04 16:20 UTCGHSA enrichment
  21. 2026-09-04 11:19 UTCEG score recompute
  22. 2026-09-04 10:24 UTCEG score recompute
  23. 2026-09-04 10:23 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-85534?
CVE-2026-85534 is a medium vulnerability published on September 4, 2026. 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 SETTINGSINITIALWINDOW_SIZE while that buffered read is still in…
When was CVE-2026-85534 disclosed?
CVE-2026-85534 was first published in the National Vulnerability Database on September 4, 2026, with the most recent update on September 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-85534 actively exploited?
CVE-2026-85534 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 75.3% of all scored CVEs.
What is the CVSS score of CVE-2026-85534?
CVE-2026-85534 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2026-85534?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-85534, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-85534

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