CVE-2026-6994: Envoy Query Parameter Injection RCE Flaw

CVE-2026-6994 Overview

A query parameter injection vulnerability has been identified in Envoy proxy up to version 1.33.0. The vulnerability exists in the params.add function within the file source/extensions/filters/http/header_mutation/header_mutation.cc, which is part of the Query Parameter Handler component. This weakness allows attackers to manipulate query parameters in a way that results in injection attacks. The vulnerability can be exploited remotely over the network, making it a significant concern for organizations running affected Envoy deployments.

Critical Impact

Remote attackers can exploit this injection vulnerability (CWE-74) in Envoy's Query Parameter Handler to manipulate HTTP requests, potentially leading to unauthorized data access or request manipulation in service mesh environments.

Affected Products

• Envoy versions up to 1.33.0
• Envoy deployments using the Header Mutation HTTP filter
• Service mesh implementations utilizing affected Envoy proxy versions

Discovery Timeline

• April 25, 2026 - CVE-2026-6994 published to NVD
• April 27, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6994

Vulnerability Analysis

This vulnerability is classified as an Injection vulnerability (CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component). The flaw resides in Envoy's HTTP Header Mutation filter, specifically in how the params.add function handles query parameter processing.

When query parameters are processed through the Header Mutation filter, insufficient validation or sanitization allows specially crafted input to be injected into the request processing pipeline. This can enable attackers to manipulate the behavior of downstream components that consume these parameters. The network-based attack vector means exploitation can occur remotely without requiring local access to the target system.

The vulnerability affects the header mutation extension, which is commonly used in service mesh configurations to modify HTTP headers and query parameters as requests flow through the Envoy proxy.

Root Cause

The root cause of this vulnerability lies in improper input neutralization within the params.add function in source/extensions/filters/http/header_mutation/header_mutation.cc. The function fails to adequately sanitize or validate user-controlled input before incorporating it into query parameter processing, allowing injection of malicious content.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can craft malicious HTTP requests containing specially formatted query parameters that, when processed by the vulnerable Header Mutation filter, result in injection attacks. The exploitation requires low privileges and no user interaction, making it relatively straightforward for authenticated attackers to exploit.

The vulnerability manifests when the Header Mutation filter processes incoming requests. Attackers can inject malicious content through query parameters that bypass proper sanitization. For detailed technical analysis, refer to the GitHub Pull Request Discussion and GitHub Commit Changes.

Detection Methods for CVE-2026-6994

Indicators of Compromise

• Unusual query parameter patterns in HTTP requests passing through Envoy proxies
• Anomalous characters or escape sequences in query string parameters
• Unexpected behavior in downstream services processing requests from Envoy
• Log entries showing malformed or suspicious query parameter values in Header Mutation filter processing

Detection Strategies

• Monitor Envoy access logs for requests with abnormal query parameter patterns or injection signatures
• Implement Web Application Firewall (WAF) rules to detect common injection payloads in query strings
• Deploy network intrusion detection systems (NIDS) with rules targeting injection attempts in HTTP traffic
• Review Envoy configuration to identify deployments using the Header Mutation HTTP filter extension

Monitoring Recommendations

• Enable verbose logging for the Header Mutation filter to capture detailed request processing information
• Set up alerting for unusual patterns in query parameter handling across Envoy proxy instances
• Monitor for increased error rates or unexpected responses from services behind affected Envoy deployments
• Implement continuous security monitoring using SentinelOne Singularity platform to detect exploitation attempts

How to Mitigate CVE-2026-6994

Immediate Actions Required

• Identify all Envoy proxy instances running versions up to 1.33.0 in your environment
• Review configurations to determine which deployments utilize the Header Mutation HTTP filter
• Plan and schedule patching activities to apply the security fix
• Consider implementing additional input validation at the application layer as a defense-in-depth measure

Patch Information

A patch has been released to address this vulnerability. The fix is identified by commit hash f8f4f1e02fdc64ecd4acf2d903208dd7285ad3a4. Organizations should update their Envoy deployments to incorporate this security patch. The patch details can be reviewed at the GitHub Commit Changes page. Additional context on the fix is available in the GitHub Pull Request Discussion.

Workarounds

• Disable the Header Mutation HTTP filter if it is not essential for your deployment
• Implement upstream input validation to sanitize query parameters before they reach Envoy
• Deploy a Web Application Firewall (WAF) in front of Envoy to filter potentially malicious requests
• Use network segmentation to limit exposure of vulnerable Envoy instances to untrusted networks

# Configuration example - Disable Header Mutation filter temporarily
# In envoy.yaml, comment out or remove the header_mutation filter
# from the http_filters section until patching is complete

# Example filter chain modification:
# http_filters:
#   # - name: envoy.filters.http.header_mutation  # Temporarily disabled
#   - name: envoy.filters.http.router
#     typed_config:
#       "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router