CVE-2022-1996: Go-restful Auth Bypass Vulnerability

CVE-2022-1996 Overview

CVE-2022-1996 is an Authorization Bypass Through User-Controlled Key vulnerability in the GitHub repository emicklei/go-restful prior to version v3.8.0. This vulnerability exists in the Cross-Origin Resource Sharing (CORS) filter implementation, where improper validation of the Origin header allows attackers to bypass domain restrictions and access protected resources.

Critical Impact

This vulnerability allows unauthenticated attackers to bypass CORS domain restrictions via network access, potentially leading to unauthorized access to sensitive data and the ability to modify protected resources without any user interaction.

Affected Products

• go-restful versions prior to v3.8.0
• Fedora 35
• Fedora 36

Discovery Timeline

• 2022-06-08 - CVE-2022-1996 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-1996

Vulnerability Analysis

The vulnerability resides in the CORS filter implementation within cors_filter.go of the go-restful library. The flaw stems from improper validation of the AllowedDomains configuration, where the library used regular expression matching for allowed domain entries. This approach allowed attackers to craft malicious Origin headers that could match allowed domain patterns in unintended ways, effectively bypassing CORS restrictions.

The go-restful library is a widely-used Go package for building RESTful web services, making this vulnerability particularly impactful for organizations running microservices and API backends built with this framework. When CORS protections are bypassed, attackers can make cross-origin requests that should otherwise be blocked, potentially accessing sensitive API endpoints and user data.

Root Cause

The root cause is classified as CWE-639: Authorization Bypass Through User-Controlled Key. The vulnerability exists because the CORS filter allowed regular expression patterns in the AllowedDomains configuration, enabling attackers to manipulate the Origin header to match these patterns inappropriately. The implementation failed to use exact matching for domain validation, creating an exploitable condition where user-controlled input (the Origin header) could be crafted to bypass authorization controls.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a target application using a vulnerable version of go-restful with CORS restrictions configured
2. Crafting a malicious Origin header that exploits the regular expression matching behavior
3. Sending cross-origin requests with the crafted Origin header to bypass domain restrictions
4. Accessing protected API endpoints and resources that should be restricted by CORS policy

The security patch addresses this by implementing exact matching of allowed domain entries and introducing an optional AllowedDomainFunc for custom validation logic:

 // http://enable-cors.org/server.html
 // http://www.html5rocks.com/en/tutorials/cors/#toc-handling-a-not-so-simple-request
 type CrossOriginResourceSharing struct {
-	ExposeHeaders  []string // list of Header names
-	AllowedHeaders []string // list of Header names
-	AllowedDomains []string // list of allowed values for Http Origin. An allowed value can be a regular expression to support subdomain matching. If empty all are allowed.
+	ExposeHeaders []string // list of Header names
+
+	// AllowedHeaders is alist of Header names. Checking is case-insensitive.
+	// The list may contain the special wildcard string ".*" ; all is allowed
+	AllowedHeaders []string
+
+	// AllowedDomains is a list of allowed values for Http Origin.
+	// The list may contain the special wildcard string ".*" ; all is allowed
+	// If empty all are allowed.
+	AllowedDomains []string
+
+	// AllowedDomainFunc is optional and is a function that will do the check
+	// when the origin is not part of the AllowedDomains and it does not contain the wildcard ".*".
+	AllowedDomainFunc func(origin string) bool
+
+	// AllowedMethods is either empty or has a list of http methods names. Checking is case-insensitive.
 	AllowedMethods []string
 	MaxAge         int // number of seconds before requiring new Options request
 	CookiesAllowed bool

Source: GitHub Commit

Detection Methods for CVE-2022-1996

Indicators of Compromise

• Unexpected cross-origin requests in application logs from domains not in the allowed list
• Anomalous Access-Control-Allow-Origin response headers returning values that should be blocked
• API access patterns from origins that do not match legitimate application domains
• Increased authentication failures or unauthorized data access from cross-origin sources

Detection Strategies

• Review application dependency manifests (go.mod, go.sum) for go-restful versions below v3.8.0
• Implement web application firewall (WAF) rules to detect and alert on suspicious Origin header patterns
• Audit CORS response headers in production environments to identify unexpected allowed origins
• Enable detailed logging for CORS preflight requests and cross-origin API calls

Monitoring Recommendations

• Monitor HTTP request logs for unusual Origin headers, particularly those with special characters or patterns
• Set up alerts for CORS-related security events in application monitoring systems
• Track dependency versions across development and production environments using software composition analysis (SCA) tools
• Implement runtime application self-protection (RASP) to detect CORS bypass attempts

How to Mitigate CVE-2022-1996

Immediate Actions Required

• Upgrade go-restful to version v3.8.0 or later immediately
• Audit all applications using go-restful for vulnerable versions in the dependency tree
• Review and strengthen CORS configurations to use explicit domain allow-lists
• Implement additional authorization checks at the API layer as defense-in-depth

Patch Information

The vulnerability has been fixed in go-restful version v3.8.0. The patch implements exact matching for allowed domain entries instead of regular expression matching, and introduces an optional AllowedDomainFunc callback for custom validation logic when needed. Organizations should update their dependencies to the patched version as soon as possible.

For detailed information, refer to:

• GitHub Commit with Security Fix
• Huntr Bounty Report
• NetApp Security Advisory

Workarounds

• Implement additional server-side authorization checks that do not rely solely on CORS for security
• Use an explicit whitelist of allowed origins and validate the Origin header at the application layer
• Deploy a reverse proxy or API gateway with strict CORS enforcement as an additional layer
• Consider using the AllowedDomainFunc callback (in patched versions) for strict custom validation logic

# Update go-restful dependency to patched version
go get github.com/emicklei/go-restful/v3@v3.8.0

# Verify the updated version in go.mod
go list -m github.com/emicklei/go-restful/v3

# Run dependency audit
go list -m -versions github.com/emicklei/go-restful/v3