CVE-2026-48521

MEDIUMPre-NVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.7% (51st percentile of EPSS-scored CVEs). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Elevated
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.7%CVSS: 5.9Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's ProdClusterManagerFactory::allocateConnPool dereferences transport_socket_options while selecting an HTTP/3 connection pool without first checking whether the pointer is null. LoadBalancerContext implementations used by synthetic, mirror, health-check, and async-client calls can return no transport-socket options. With auto_config and HTTP/3 enabled, routine traffic reaching one of those contexts can crash an Envoy worker. The relevant scope boundary is that the affected branch requires HTTP/3 in the protocol set and a context that supplies no transport-socket options. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

CVSS v3
5.9
EG Score
5.9MEDIUMmedium confidence
EG Risk
43
EG Risk 43/100CISA SSVC

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%
Exploitation40% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.7%
EPSS %ILE
51st
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

September 21, 2026

Last Modified

September 23, 2026

Advisory Details (9)

Auto-updated Sep 21, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_commit, github_release.
github_release Patch Available

v1.39.1

Patch available: envoyproxy/envoy v1.39.1

https://github.com/envoyproxy/envoy/releases/tag/v1.39.1
github_release Patch Available

v1.38.4

Patch available: envoyproxy/envoy v1.38.4

https://github.com/envoyproxy/envoy/releases/tag/v1.38.4
github_release Patch Available

v1.37.6

Patch available: envoyproxy/envoy v1.37.6

https://github.com/envoyproxy/envoy/releases/tag/v1.37.6
github_release Patch Available

v1.36.10

Patch available: envoyproxy/envoy v1.36.10

https://github.com/envoyproxy/envoy/releases/tag/v1.36.10
github_commit

commit f5436f44103f (envoyproxy/envoy)

Fix landed in envoyproxy/envoy commit f5436f44103f — awaiting tagged release

https://github.com/envoyproxy/envoy/commit/f5436f44103fb14cb8ba42a8db0f54a06c98c45a
github_commit

commit e7b4839beef7 (envoyproxy/envoy)

Fix landed in envoyproxy/envoy commit e7b4839beef7 — awaiting tagged release

https://github.com/envoyproxy/envoy/commit/e7b4839beef7f43594ce8e94c4563c80db04a8a7
github_commit

commit cec4899acf03 (envoyproxy/envoy)

Fix landed in envoyproxy/envoy commit cec4899acf03 — awaiting tagged release

https://github.com/envoyproxy/envoy/commit/cec4899acf03cf551f28611a5f32385648d95f96
github_commit

commit 8ef2da8527fc (envoyproxy/envoy)

Fix landed in envoyproxy/envoy commit 8ef2da8527fc — awaiting tagged release

https://github.com/envoyproxy/envoy/commit/8ef2da8527fcd17388b046c1add4fb47fb5d0868
github Patch Available🟡 PoC Available

HTTP/3 connection pool selection null-derefs in ProdClusterManagerFactory::allocateConnPool when transport_socket_options is null · Advisory · envoyproxy/envoy · GitHub

https://github.com/envoyproxy/envoy/security/advisories/GHSA-5vff-j9p4-38j3

Vendor Advisories for CVE-2026-48521(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 13× in last 7d / 24× 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. 2026-10-04 04:32 UTCEG score recompute
  2. 2026-10-03 14:25 UTCEPSS rescore
  3. 2026-10-03 05:49 UTCEG score recompute
  4. 2026-10-02 06:59 UTCEG score recompute
  5. 2026-10-01 19:50 UTCEPSS rescore
  6. 2026-10-01 08:16 UTCEG score recompute
  7. 2026-09-30 15:03 UTCEPSS rescore
  8. 2026-09-30 09:34 UTCEG score recompute
  9. 2026-09-29 10:44 UTCEG score recompute
  10. 2026-09-28 13:51 UTCEPSS rescore
  11. 2026-09-28 12:02 UTCEG score recompute
  12. 2026-09-27 13:48 UTCEPSS rescore
  13. 2026-09-27 13:19 UTCEG score recompute
  14. 2026-09-26 15:59 UTCEPSS rescore
  15. 2026-09-26 14:37 UTCEG score recompute
  16. 2026-09-26 00:27 UTCEPSS rescore
  17. 2026-09-24 17:09 UTCEG score recompute
  18. 2026-09-23 18:26 UTCEG score recompute
  19. 2026-09-23 17:53 UTCEPSS rescore
  20. 2026-09-22 19:00 UTCEG score recompute
  21. 2026-09-21 20:18 UTCEG score recompute
  22. 2026-09-21 20:05 UTCEG score recompute
  23. 2026-09-21 19:55 UTCEG score recompute
  24. 2026-09-21 19:55 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-48521?
CVE-2026-48521 is a medium vulnerability published on September 21, 2026. Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's ProdClusterManagerFactory::allocateConnPool dereferences transportsocketoptions while selecting an HTTP/3 connection pool without first checking whether the…
When was CVE-2026-48521 disclosed?
CVE-2026-48521 was first published on September 21, 2026, with the most recent update on September 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-48521 actively exploited?
CVE-2026-48521 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.7% probability of exploitation in the next 30 days (51st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-48521?
CVE-2026-48521 has a CVSS base score of 5.9 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-48521?
A fix for CVE-2026-48521 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-48521 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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