CVE-2025-69287: BSV Blockchain SDK Auth Bypass Flaw

CVE-2025-69287 Overview

A cryptographic vulnerability has been identified in the BSV Blockchain TypeScript SDK's BRC-104 authentication implementation. The flaw causes incorrect signature data preparation, resulting in signature incompatibility between SDK implementations and potential authentication bypass scenarios. This vulnerability affects the mutual authentication mechanism used to establish trust between peers in blockchain applications built with the TypeScript SDK.

Critical Impact

The vulnerability enables cross-implementation authentication failures and potential authentication bypass, allowing attackers to circumvent security checks in applications relying on BRC-104 mutual authentication.

Affected Products

• BSV Blockchain TypeScript SDK versions prior to 2.0.0
• Applications using BRC-104 mutual authentication between TypeScript and Go/Python SDK implementations

Discovery Timeline

• 2026-02-18 - CVE CVE-2025-69287 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2025-69287

Vulnerability Analysis

The vulnerability resides in the Peer.ts file of the TypeScript SDK, specifically within the processInitialRequest and processInitialResponse methods responsible for preparing signature data during BRC-104 mutual authentication. The core issue stems from improper handling of nonce concatenation during cryptographic signature generation.

The TypeScript SDK incorrectly prepared signature data by first concatenating base64-encoded nonce strings (message.initialNonce + sessionNonce) and then decoding the concatenated base64 string using base64ToBytes(concatenatedString). This flawed approach produced approximately 32-34 bytes of signature data instead of the correct 64 bytes that other SDK implementations (Go and Python) expected.

BRC-104 authentication relies on cryptographic signatures to establish mutual trust between peers. When signature data preparation is incorrect, signatures generated by the TypeScript SDK don't match those expected by Go/Python SDKs, causing cross-implementation authentication to fail. An attacker could potentially exploit this inconsistency to bypass authentication checks in multi-SDK environments.

Root Cause

The root cause is classified under CWE-573 (Improper Following of Specification). The TypeScript SDK implementation deviated from the BRC-104 specification by incorrectly handling the byte array concatenation of nonces. Instead of separately decoding each base64-encoded nonce and concatenating the resulting byte arrays, the implementation concatenated the base64 strings first and then decoded, producing incorrect signature data length and content.

Attack Vector

The vulnerability is exploitable over the network and requires user interaction. An attacker could exploit this vulnerability in scenarios where:

1. A system relies on cross-implementation authentication between TypeScript SDK clients and Go/Python SDK servers
2. The attacker can initiate or intercept authentication handshakes
3. The signature verification process can be manipulated due to the inconsistent data preparation

The incorrect signature data length (32-34 bytes vs 64 bytes) creates an asymmetry that could be leveraged to craft authentication requests that behave differently across SDK implementations.

 
     // Create signature
     const { signature } = await this.wallet.createSignature({
-      data: Peer.base64ToBytes(message.initialNonce + sessionNonce),
+      data: [
+        ...Peer.base64ToBytes(message.initialNonce),
+        ...Peer.base64ToBytes(sessionNonce)
+      ],
       protocolID: [2, 'auth message signature'],
       keyID: `${message.initialNonce} ${sessionNonce}`,
       counterparty: message.identityKey

Source: GitHub Commit d8cf693

Detection Methods for CVE-2025-69287

Indicators of Compromise

• Authentication failures between TypeScript SDK clients and Go/Python SDK servers in BRC-104 mutual authentication flows
• Signature verification errors with unexpected data length (32-34 bytes instead of 64 bytes)
• Anomalous authentication patterns where requests succeed against one SDK implementation but fail against others

Detection Strategies

• Monitor application logs for BRC-104 authentication failures, particularly signature mismatch errors
• Implement signature data length validation to detect incorrectly formatted authentication requests
• Track authentication success/failure rates across different SDK implementation pairs
• Review network traffic for authentication handshakes with inconsistent nonce handling

Monitoring Recommendations

• Enable verbose logging for BRC-104 authentication processes to capture signature generation details
• Set up alerts for elevated rates of authentication failures between SDK implementations
• Monitor for unusual authentication patterns that may indicate exploitation attempts

How to Mitigate CVE-2025-69287

Immediate Actions Required

• Upgrade the BSV Blockchain TypeScript SDK to version 2.0.0 or later immediately
• Review application logs for any historical authentication anomalies that may indicate past exploitation
• Verify that all SDK implementations in your environment are using compatible versions
• Test cross-implementation authentication after upgrading to confirm proper mutual authentication

Patch Information

The vulnerability has been fixed in BSV Blockchain TypeScript SDK version 2.0.0. The fix ensures all SDKs now produce identical cryptographic signatures by correctly decoding each nonce separately before concatenating the resulting byte arrays. For detailed patch information, refer to the GitHub Security Advisory GHSA-vjpq-xx5g-qvmm and the commit d8cf6930028372079d977138ae9eaa03ae2f50bb.

Workarounds

• If immediate upgrade is not possible, consider implementing additional authentication layers outside of BRC-104
• Temporarily restrict cross-implementation authentication to single-SDK environments where possible
• Implement application-level signature validation that checks for correct data length (64 bytes)

# Configuration example
# Upgrade BSV Blockchain TypeScript SDK to patched version
npm update @bsv/sdk@2.0.0

# Verify installed version
npm list @bsv/sdk