5.3

CVE-2026-26309: envoyproxy envoy Off-by-one Error

CVSS: 5.3v3.1MediumAnalyzed
AliasesGHSA-56cj-wgg3-x943BIT-envoy-2026-26309
Published 10-03-2026Last modified 10-03-2026
Open JSON

Vulnerability summary

CVE-2026-26309 is a medium (CVSS 5.3) Off-by-one Error vulnerability in envoyproxy envoy. EPSS estimates a 0.43% chance of exploitation in the next 30 days, higher than 36.3% of scored vulnerabilities. 1 public exploit is recorded.

Overall risk
31/100
0100
Medium · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.43%
0%100%
Low · +0.07 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits1github

Timeline

  1. 10-03-2026
    PublishedVulnerability first disclosed.
  2. 10-03-2026
    Last modifiedVulnerability information updated.

Description

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.

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

0.43%

Chance of exploitation in the next 30 days

Percentile

36%

Versus all other CVEs

30-day change

+0.07 pp

From 0.36% on 21-09-2026

21-09-202621-10-2026
EPSS score
0.43%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

1 found
  • githubUnverified

    Envoy

    Maturity: poc

Weaknesses

CWE · root cause

Affected systems

Envoyproxy1 product
  • envoy≥ 1.37.0, < 1.37.1 | ≥ 1.35.0, < 1.35.9 | < 1.34.13 | ≥ 1.35.0, < 1.35.8 | ≥ 1.36.0, < 1.36.5 | 1.37.0
Github.com/envoyproxy1 product
  • envoy1.37.0 | ≥ 1.36.0, ≤ 1.36.4 | ≥ 1.35.0, ≤ 1.35.8 | ≤ 1.34.12

2 vendors · 2 products

References

3 links