CVE-2024-53271: Envoyproxy Envoy DOS Vulnerability

CVE-2024-53271 Overview

CVE-2024-53271 affects Envoy, a cloud-native high-performance edge, middle, and service proxy widely deployed in service mesh and API gateway architectures. Affected versions do not properly handle HTTP/1.1 non-101 1xx informational responses. This improper handling propagates downstream and causes failures in networked devices that depend on Envoy for traffic mediation. The issue maps to [CWE-670: Always-Incorrect Control Flow Implementation]. The Envoy project addressed the flaw in versions 1.31.5 and 1.32.3. No workarounds exist, so operators must upgrade affected deployments.

Critical Impact
A remote attacker can trigger downstream service failures by inducing Envoy to mishandle HTTP/1.1 non-101 1xx responses, resulting in availability loss across networked applications behind the proxy.

Affected Products

Envoy versions prior to 1.31.5 on the 1.31.x branch
Envoy versions prior to 1.32.3 on the 1.32.x branch
Deployments using Envoy as an edge, middle, or service proxy for HTTP/1.1 traffic

Discovery Timeline

2024-12-18 - CVE-2024-53271 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-53271

Vulnerability Analysis

The vulnerability resides in Envoy's HTTP/1.1 response processing path. HTTP/1.1 defines several informational 1xx status codes, including 100 Continue, 102 Processing, and 103 Early Hints. Envoy correctly handles the 101 Switching Protocols case but mishandles other 1xx responses. When an upstream server returns a non-101 1xx status, Envoy's control flow diverges from expected behavior, corrupting the response stream state seen by downstream clients.

Downstream devices depending on the proxy then observe malformed or unexpected sequences, leading to connection failures and service disruption. The flaw is exploitable across a network with low attack complexity, requiring no privileges, though user interaction on the requesting client is a factor per the CVSS vector.

Root Cause

The root cause is incorrect control-flow logic in the HTTP/1.1 codec responsible for forwarding informational responses. The codec assumed 1xx responses would be limited to 101 Switching Protocols in the paths it handled and did not correctly account for other informational status codes emitted by upstream servers. The fix, delivered in commit da56f6da63079baecef9183436ee5f4141a59af8, adjusts response handling to correctly process non-101 1xx responses before forwarding them.

Attack Vector

An attacker able to influence an upstream server response, or an attacker operating a malicious upstream, can return a non-101 1xx status to trigger the mishandling. The malformed forwarded response then breaks downstream HTTP consumers. Because Envoy is typically deployed at the network edge or in service meshes, exploitation cascades to the applications it fronts. See the GitHub Security Advisory GHSA-rmm5-h2wv-mg4f for full technical detail.

No public proof-of-concept is available and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score is 0.61% at the 44.7 percentile.

Detection Methods for CVE-2024-53271

Indicators of Compromise

Unexpected connection resets or protocol errors reported by services sitting behind Envoy after upstream responses containing 1xx status codes
Envoy access logs showing abnormal termination flags on HTTP/1.1 streams that carried informational responses
Client-side HTTP parser errors correlated with upstream 102 Processing or 103 Early Hints responses

Detection Strategies

Inventory all Envoy instances and compare running versions against fixed releases 1.31.5 and 1.32.3 using package management or admin endpoint /server_info
Enable and review Envoy stats such as http1.response_flood and downstream/upstream connection termination counters for anomalies
Correlate upstream HTTP/1.1 responses containing non-101 1xx codes with downstream failure events in centralized logs

Monitoring Recommendations

Ingest Envoy access logs and admin metrics into a centralized logging or SIEM platform for continuous version and behavior monitoring
Alert on spikes in 5xx responses or connection resets from services fronted by Envoy following upstream configuration changes
Track HTTP/1.1 codec error metrics and upstream response status distributions per cluster

How to Mitigate CVE-2024-53271

Immediate Actions Required

Upgrade Envoy to version 1.31.5 for the 1.31.x branch or 1.32.3 for the 1.32.x branch as soon as maintenance windows allow
Identify all managed and embedded Envoy deployments, including service mesh sidecars such as Istio and Consul, and prioritize upgrades for internet-facing proxies
Validate upstream services to ensure they only emit 1xx responses that are strictly required by application logic

Patch Information

The fix is committed in the Envoy repository at commit da56f6da63079baecef9183436ee5f4141a59af8 and shipped in Envoy releases 1.31.5 and 1.32.3. Downstream distributions that embed Envoy, including service mesh control planes, should be updated to versions that incorporate these fixes. Refer to the Envoy Security Advisory GHSA-rmm5-h2wv-mg4f for full release guidance.

Workarounds

No workarounds exist per the vendor advisory; upgrading Envoy is the only supported remediation
Operators can reduce exposure by restricting which upstream services are permitted to emit non-101 1xx responses until patched builds are deployed

bash

# Verify the running Envoy version against the fixed releases
envoy --version

# Example: query the admin interface for version and build info
curl -s http://127.0.0.1:9901/server_info | grep -E 'version|revision'

# Confirm the deployed version is >= 1.31.5 or >= 1.32.3