CVE-2025-64763 — envoy
LOWCVE-2025-64763 is a low-severity (CVSS 3.7) CWE-693 vulnerability in github.com/envoyproxy/envoy. A fix is available for github.com/envoyproxy/envoy — see the affected versions and patch details below.
Envoy forwards early CONNECT data in TCP proxy mode
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-64763.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-64763 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/envoyproxy/envoy🐹github.com/envoyproxy/envoy🐹github.com/envoyproxy/envoy🐹github.com/envoyproxy/envoyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/envoyproxy/envoy | ≥ 1.36.0&&< 1.36.3 | 1.36.3go get github.com/envoyproxy/envoy@v1.36.3 |
| 🐹Go | github.com/envoyproxy/envoy | ≥ 1.35.0&&< 1.35.7 | 1.35.7go get github.com/envoyproxy/envoy@v1.35.7 |
| 🐹Go | github.com/envoyproxy/envoy | ≥ 1.34.0&&< 1.34.11 | 1.34.11go get github.com/envoyproxy/envoy@v1.34.11 |
| 🐹Go | github.com/envoyproxy/envoy | all versions | 1.33.13go get github.com/envoyproxy/envoy@v1.33.13 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/envoyproxy/envoy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/envoyproxy/envoy to 1.36.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-64763 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-64763 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-64763. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-64763 in your dependencies?
O3 Security finds CVE-2025-64763 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.