CVE-2020-8169: Haxx Curl Information Disclosure Flaw

CVE-2020-8169 Overview

CVE-2020-8169 is an information disclosure vulnerability affecting curl versions 7.62.0 through 7.70.0. The vulnerability allows a partial password to be leaked over the network and to DNS server(s) when processing specially crafted URLs. This flaw exists in the URL parsing functionality of the curl library, which is widely used for transferring data across networks.

Critical Impact

Partial credential leakage to network and DNS servers could enable attackers to intercept sensitive authentication data, potentially leading to account compromise or further network intrusion.

Affected Products

• Haxx curl versions 7.62.0 through 7.70.0
• Siemens SIMATIC TIM 1531 IRC Firmware
• Siemens SINEC Infrastructure Network Services
• Debian Linux 10.0
• Splunk Universal Forwarder (multiple versions including 9.1.0)

Discovery Timeline

• 2020-12-14 - CVE-2020-8169 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-8169

Vulnerability Analysis

This vulnerability is classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The flaw resides in curl's URL parsing mechanism, specifically in how it handles URLs containing credentials. When a URL includes embedded authentication credentials, the vulnerable versions of curl improperly process certain malformed URLs, causing a portion of the password to be transmitted in cleartext to network entities and DNS servers.

The vulnerability is particularly concerning because DNS queries are typically unencrypted and may be logged by DNS servers, ISPs, or network monitoring equipment. This means that partial password data could be captured and stored in multiple locations without the user's knowledge.

Root Cause

The root cause of this vulnerability lies in improper input validation within curl's URL parser. When processing URLs with embedded credentials (in the format protocol://user:password@host/path), certain edge cases were not handled correctly, leading to portions of the password being included in DNS lookups or network traffic where they should not appear.

The URL parser failed to properly sanitize or redact sensitive credential information before performing DNS resolution, resulting in the information disclosure condition.

Attack Vector

The attack vector for this vulnerability is network-based and requires no user interaction or special privileges. An attacker positioned to observe network traffic or with access to DNS query logs could potentially capture leaked password fragments. Attack scenarios include:

1. Passive Network Monitoring: An attacker on the same network segment could capture leaked credentials through packet inspection
2. DNS Server Compromise: Malicious or compromised DNS servers could log and collect partial password data
3. Man-in-the-Middle Position: Attackers with MITM capabilities could intercept the leaked information during DNS resolution

The vulnerability can be triggered when a user or application uses curl to access URLs containing embedded authentication credentials that are malformed in a specific way that triggers the improper parsing behavior.

Detection Methods for CVE-2020-8169

Indicators of Compromise

• Unusual DNS queries containing what appear to be password fragments or credential-like strings
• Network traffic showing authentication data in unexpected protocol layers
• Log entries in DNS servers containing non-standard characters or encoded credential patterns
• Applications using vulnerable curl versions (7.62.0 - 7.70.0) making requests with embedded credentials

Detection Strategies

• Monitor DNS query logs for anomalous strings that may indicate credential leakage
• Implement network traffic analysis to detect authentication data appearing in cleartext DNS requests
• Perform software composition analysis to identify systems running vulnerable curl versions
• Review application logs for URLs with embedded credentials being processed by affected curl versions

Monitoring Recommendations

• Deploy network intrusion detection systems (NIDS) with signatures for detecting credential-like patterns in DNS traffic
• Enable comprehensive DNS logging and implement automated analysis for sensitive data exposure
• Monitor curl version deployments across the infrastructure using asset inventory tools
• Implement Security Information and Event Management (SIEM) correlation rules for credential leakage patterns

How to Mitigate CVE-2020-8169

Immediate Actions Required

• Upgrade curl to version 7.71.0 or later immediately on all affected systems
• Audit applications and scripts for URLs containing embedded credentials and refactor to use safer authentication methods
• Review DNS query logs for potential historical credential leakage
• Implement network segmentation to limit exposure of systems that cannot be immediately patched

Patch Information

The curl project addressed this vulnerability in version 7.71.0. Organizations should update to this version or later to remediate the issue. Vendor-specific patches are also available:

• Haxx curl: Upgrade to version 7.71.0 or later - see the Curl CVE-2020-8169 Documentation
• Siemens Products: Apply patches per Siemens Security Advisory SSA-389290 and SSA-200951
• Debian Linux: Apply security update per Debian Security Advisory DSA-4881
• Splunk Universal Forwarder: Update to patched versions as specified in vendor documentation

Workarounds

• Avoid using URLs with embedded credentials; use curl's --user option or .netrc files instead
• Implement network-level controls to prevent DNS queries from leaving trusted network boundaries
• Use encrypted DNS (DNS-over-HTTPS or DNS-over-TLS) to protect any potentially leaked data in transit
• Deploy Web Application Firewalls (WAFs) or proxy servers that sanitize outbound URLs

# Example: Safer authentication method using curl
# Instead of: curl https://user:password@example.com/api
# Use the --user option:
curl --user "username:password" https://example.com/api

# Or use a .netrc file for credential storage
echo "machine example.com login username password yourpassword" >> ~/.netrc
chmod 600 ~/.netrc
curl --netrc https://example.com/api