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CVE-2026-73549 Envoyproxy CVE debrief

CVE-2026-73549 is a vulnerability in Envoy, an open-source edge and service proxy, which can cause a process termination due to improper handling of scoped IPv6 addresses in the Utility::copyInternetAddressAndPort and QUIC client-address paths. This issue affects Envoy versions prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, particularly in ORIGINAL_DST transparent-proxy deployments or QUIC connection paths. The vulnerability can lead to service disruption, and defenders should prioritize patching or upgrading to fixed versions to prevent potential process termination.

Vendor
Envoyproxy
Product
Envoy
CVSS
MEDIUM 5.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-21
Original CVE updated
2026-10-05
Advisory published
2026-09-21
Advisory updated
2026-10-05

Who should care

Defenders and administrators of Envoy instances, particularly those using ORIGINAL_DST transparent-proxy deployments or QUIC connection paths, should assess their exposure and prioritize patching or upgrading to fixed versions.

Why it matters

CVE-2026-73549 is a vulnerability in Envoy that can cause process termination due to improper handling of scoped IPv6 addresses. Defenders should prioritize patching or upgrading to fixed versions to prevent potential service disruption.

  • Potential process termination due to improper handling of scoped IPv6 addresses
  • Possible service disruption in ORIGINAL_DST transparent-proxy deployments
  • Need for verification of affected versions and configurations
  • Priority for patching or upgrading to fixed versions

Technical summary

The vulnerability is caused by the improper handling of scoped IPv6 addresses in Envoy's Utility::copyInternetAddressAndPort and QUIC client-address paths. This can lead to a process termination when a kernel-provided scoped IPv6 destination is encountered in ORIGINAL_DST transparent-proxy deployments or affected QUIC connection paths. The issue is fixed in Envoy versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1. Defenders should prioritize patching or upgrading to fixed versions to prevent potential service disruption.

Defensive priority

Defenders should prioritize patching or upgrading to fixed versions of Envoy, specifically versions 1.36.10, 1.37.6, 1.38.4, or 1.39.1, to prevent potential process termination.

Recommended defensive actions

  • Upgrade to Envoy version 1.36.10, 1.37.6, 1.38.4, or 1.39.1
  • Review and update configurations for ORIGINAL_DST transparent-proxy deployments
  • Monitor for potential process termination issues
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
  • Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
  • Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The vulnerability is caused by the improper handling of scoped IPv6 addresses in Envoy's Utility::copyInternetAddressAndPort and QUIC client-address paths. This can lead to a process termination when a kernel-provided scoped IPv6 destination is encountered in ORIGINAL_DST transparent-proxy deployments or affected QUIC connection paths.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-73549 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-73549

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-73549 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-73549

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.