# CVE-2026-26309: Envoy affected by off-by-one write in JsonEscaper::escapeString()

Source: https://junglewise.ai/threats/cve-2026-26309-envoy-affected-by-off-by-one-write-in-jsonescaper-escapestring  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-10  
License: CC BY 4.0 with a link back

CVE-2026-26309 · Severity: low · CVSS 3.1 · Published 2026-03-10

Envoy affected by off-by-one write in JsonEscaper::escapeString()

Technologies: [github.com/envoyproxy/envoy (Go)](https://junglewise.ai/threats/technologies/github-com-envoyproxy-envoy). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-26309 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-26309 being exploited in the wild.

**How severe is CVE-2026-26309?** Low severity, with a CVSS score of 3.1, published 10 March 2026.

**Which products and versions are affected?** github.com/envoyproxy/envoy (Go) SEMVER:introduced=1.36.0,last_affected=1.36.4.

**Is there a fix for CVE-2026-26309?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2026-26309?** Check whether you run github.com/envoyproxy/envoy (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- github.com/envoyproxy/envoy (Go) SEMVER:introduced=1.36.0,last_affected=1.36.4

## Identifiers

- CVE-2026-26309
- GHSA-56cj-wgg3-x943

## Related threats

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- [Envoy: HTTP - filter chain execution on reset streams causing UAF crash](https://junglewise.ai/threats/cve-2026-26311-envoy-http-filter-chain-execution-on-reset-streams-causing-uaf)
- [Envoy RBAC header validation bypass via multi-value concatenation](https://junglewise.ai/threats/cve-2026-26308-envoy-rbac-header-validation-bypass-via-multi-value-concatenation)
- [Envoy vulnerable to crash for scoped ip address during DNS](https://junglewise.ai/threats/cve-2026-26310-envoy-vulnerable-to-crash-for-scoped-ip-address-during-dns)
- [Envoy forwards early CONNECT data in TCP proxy mode](https://junglewise.ai/threats/cve-2025-64763-envoy-forwards-early-connect-data-in-tcp-proxy-mode)