Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.
CVE-2026-26309
MEDIUMNVD 5.35.3—Trending — 3 sources updated this week
EchelonGraph scoreMEDIUM confidence
Score 5.3 from GitHub Security Advisory published 2026-03-10. the CNA's CVSS baseline 5.3; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: cna:github_m, ghsa
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 5.3
- EG Score
- 5.3(medium)
- EG Risk
- 39(Track)EG Risk 39/100SSVC: 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 computedSeverity53% × 45%Exploitation0% × 40%Automatability100% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 29%
- KEV
- Not listed
Published
March 10, 2026
Last Modified
June 17, 2026
References (1)
- security-advisories@githubhttps://github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943
Vendor Advisories for CVE-2026-26309(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Patch Availability(1)
| Vendor / Ecosystem | Fixed in / Patch | Released | Source |
|---|---|---|---|
| go | github.com/envoyproxy/envoy | — | ghsa |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 3× in last 7d / 3× 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.
- 2026-07-27 12:53 UTCEG score recompute
- 2026-07-27 12:53 UTCGHSA enrichment
- 2026-07-27 12:50 UTCOSV refresh
Frequently asked(5)
What is CVE-2026-26309?
CVE-2026-26309 is a medium vulnerability published on March 10, 2026. Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the…
When was CVE-2026-26309 disclosed?
CVE-2026-26309 was first published in the National Vulnerability Database on March 10, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-26309 actively exploited?
CVE-2026-26309 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 70.9% of all scored CVEs.
What is the CVSS score of CVE-2026-26309?
CVE-2026-26309 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-26309?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-26309, 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
Explore the affected products and dependency analysis for CVE-2026-26309
Is Your Infrastructure Affected by CVE-2026-26309?
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