CVE-2021-3114: Golang Go Cryptographic Vulnerability

CVE-2021-3114 Overview

CVE-2021-3114 is an integer underflow vulnerability in the Go programming language's cryptographic library affecting the P-224 elliptic curve implementation. The vulnerability exists in crypto/elliptic/p224.go where incorrect outputs can be generated due to an underflow of the lowest limb during the final complete reduction in the P-224 field. This flaw affects Go versions before 1.14.14 and 1.15.x before 1.15.7.

The vulnerability impacts cryptographic operations that rely on the P-224 elliptic curve, potentially allowing attackers to exploit weaknesses in digital signatures or key exchange mechanisms. Since this affects the core cryptographic library, any application using Go's elliptic curve cryptography with the P-224 curve may produce incorrect cryptographic outputs, compromising the integrity and confidentiality of encrypted communications.

Critical Impact

Cryptographic operations using the P-224 elliptic curve may produce incorrect outputs, potentially undermining the security guarantees of digital signatures and key exchange protocols in Go applications.

Affected Products

• Golang Go (versions before 1.14.14 and 1.15.x before 1.15.7)
• Fedora 33
• Debian Linux 9.0 and 10.0
• NetApp Cloud Insights Telegraf Agent
• NetApp StorageGRID

Discovery Timeline

• 2021-01-26 - CVE-2021-3114 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3114

Vulnerability Analysis

The vulnerability resides in the p224Contract function within Go's crypto/elliptic/p224.go file. This function is responsible for converting a FieldElement to its unique, minimal form during elliptic curve operations. The flaw occurs during the final complete reduction step in the P-224 field arithmetic.

The P-224 curve uses a specific prime field, and field elements must be reduced to ensure they remain within valid bounds. The p224Contract function performs this reduction by carrying overflow bits between limbs (28-bit segments of the field element). The vulnerability manifests when the reduction identity is applied: a + top * 2²²⁴ = a + top * 2⁹⁶ - top.

When subtracting top from out[0], an underflow can occur if out[0] becomes negative. While the code attempts to handle this through carry-down operations, the original implementation did not guarantee that the output would be less than the prime p, leading to non-unique representations of field elements.

Root Cause

The root cause is an incomplete field reduction in the P-224 elliptic curve implementation. The p224Contract function failed to ensure that the output is strictly less than the prime modulus p. The original contract stated that on exit, in[i] < 2**28, but this was insufficient to guarantee canonical representation. The output must be both less than 2**28 for each limb AND the complete value must be less than p. This oversight in the mathematical reduction logic allowed non-canonical field element representations, which can cause incorrect cryptographic computations.

Attack Vector

This vulnerability can be exploited remotely over the network. An attacker could potentially:

1. Signature Forgery: Exploit the incorrect field reduction to generate valid-appearing signatures for arbitrary messages
2. Key Recovery: In certain scenarios, the incorrect outputs could leak information about private keys
3. Protocol Bypasses: Applications relying on P-224 curve operations for authentication or key exchange may be bypassed

The attack does not require authentication or user interaction, making it particularly concerning for TLS implementations and other network protocols using P-224.

// Security patch in src/crypto/elliptic/p224.go - crypto/elliptic: fix P-224 field reduction
 // p224Contract converts a FieldElement to its unique, minimal form.
 //
 // On entry, in[i] < 2**29
-// On exit, in[i] < 2**28
+// On exit, out[i] < 2**28 and out < p
 func p224Contract(out, in *p224FieldElement) {
 	copy(out[:], in[:])
 
+	// First, carry the bits above 28 to the higher limb.
 	for i := 0; i < 7; i++ {
 		out[i+1] += out[i] >> 28
 		out[i] &= bottom28Bits
 	}
 	top := out[7] >> 28
 	out[7] &= bottom28Bits
 
+	// Use the reduction identity to carry the overflow.
+	//
+	//   a + top * 2²²⁴ = a + top * 2⁹⁶ - top
 	out[0] -= top
 	out[3] += top << 12
 
-	// We may just have made out[i] negative. So we carry down. If we made
+	// We may just have made out[0] negative. So we carry down. If we made
 	// out[0] negative then we know that out[3] is sufficiently positive
 	// because we just added to it.
 	for i := 0; i < 3; i++ {

Source: GitHub Commit Changes

Detection Methods for CVE-2021-3114

Indicators of Compromise

• Applications compiled with vulnerable Go versions (before 1.14.14 or 1.15.x before 1.15.7) using P-224 elliptic curve operations
• Unexpected cryptographic failures or signature verification errors in Go applications
• Anomalous TLS handshake behaviors when P-224 is negotiated as the elliptic curve

Detection Strategies

• Audit Go runtime versions across all deployed applications using go version command
• Scan compiled binaries to identify the Go version used during compilation
• Monitor for applications importing crypto/elliptic package with P-224 curve usage
• Review dependency manifests (go.mod files) for vulnerable Go runtime requirements

Monitoring Recommendations

• Implement software composition analysis (SCA) to track Go runtime versions across the organization
• Set up alerts for applications using deprecated or vulnerable cryptographic curves
• Monitor cryptographic operations for unexpected failures that may indicate exploitation attempts
• Enable detailed logging for TLS negotiations to detect anomalous curve selections

How to Mitigate CVE-2021-3114

Immediate Actions Required

• Upgrade Go to version 1.14.14 or later (for 1.14.x branch)
• Upgrade Go to version 1.15.7 or later (for 1.15.x branch)
• Recompile all Go applications after upgrading the runtime
• Review cryptographic implementations for P-224 curve usage and consider migrating to stronger curves like P-256 or P-384

Patch Information

Golang has released security patches addressing this vulnerability. The fix ensures that the p224Contract function properly reduces field elements to their canonical form by guaranteeing out < p in addition to the per-limb constraints.

Patched Versions:

• Go 1.14.14 and later
• Go 1.15.7 and later

The patch is available via the GitHub Commit. Additional vendor advisories are available from Debian Security Advisory DSA-4848, Fedora Package Announcement, and NetApp Security Advisory.

Workarounds

• Disable P-224 curve usage in TLS configurations and prefer P-256, P-384, or P-521 curves
• Configure applications to reject P-224 curve negotiation where possible
• Implement additional cryptographic validation checks for applications that cannot be immediately upgraded
• Consider using alternative cryptographic libraries for P-224 operations until the Go runtime can be upgraded

# Check Go version on systems
go version

# Verify if applications use P-224 curve (search for NIST P-224 references)
grep -r "P224\|elliptic.P224" /path/to/go/source

# Update Go on Debian-based systems
sudo apt update && sudo apt upgrade golang-go

# Update Go on Fedora
sudo dnf update golang