CVE-2023-31486: HTTP::Tiny Information Disclosure Flaw

CVE-2023-31486 Overview

CVE-2023-31486 is an Improper Certificate Validation vulnerability affecting HTTP::Tiny, a lightweight HTTP client module that has been part of Perl core since version 5.13.9 and is also available as a standalone package on CPAN. The vulnerability stems from an insecure default TLS configuration where SSL/TLS certificate verification is disabled by default, requiring users to explicitly opt-in to certificate validation. This design flaw exposes applications using HTTP::Tiny to potential Man-in-the-Middle (MITM) attacks when making HTTPS connections.

Critical Impact

Applications using HTTP::Tiny for HTTPS connections are vulnerable to Man-in-the-Middle attacks by default, potentially allowing attackers to intercept, modify, or steal sensitive data transmitted over supposedly secure connections.

Affected Products

• HTTP::Tiny versions before 0.083
• Perl versions from 5.13.9 onwards (which bundle HTTP::Tiny)
• CPAN modules dependent on HTTP::Tiny for HTTPS requests

Discovery Timeline

• 2023-04-29 - CVE-2023-31486 published to NVD
• 2025-01-30 - Last updated in NVD database

Technical Details for CVE-2023-31486

Vulnerability Analysis

The vulnerability resides in HTTP::Tiny's handling of TLS/SSL connections. By design, HTTP::Tiny does not verify SSL certificates by default when establishing HTTPS connections. This means that unless a developer explicitly enables certificate verification through the verify_SSL parameter, all HTTPS connections made through HTTP::Tiny are susceptible to interception.

This architectural decision affects a significant portion of the Perl ecosystem. Since HTTP::Tiny is bundled with Perl core and serves as a lightweight alternative to more feature-rich HTTP clients like LWP::UserAgent, many CPAN modules and Perl applications unknowingly inherit this insecure default behavior. The Hackeriet analysis documented the widespread impact across CPAN modules.

The lack of certificate validation allows an attacker positioned in the network path between the client and server to present a fraudulent certificate without triggering any errors or warnings. The HTTP::Tiny client will accept this certificate and proceed with the connection, enabling the attacker to decrypt, inspect, and potentially modify the traffic in both directions.

Root Cause

The root cause is a design decision in HTTP::Tiny where the verify_SSL attribute defaults to 0 (false) rather than 1 (true). This violates the principle of secure-by-default configuration. When users instantiate HTTP::Tiny objects without explicitly setting verify_SSL => 1, their HTTPS connections do not validate server certificates against trusted Certificate Authorities.

This behavior is classified under CWE-295 (Improper Certificate Validation), which encompasses scenarios where a system fails to properly validate certificates, potentially allowing adversaries to spoof trusted entities.

Attack Vector

An attacker can exploit this vulnerability through a network-based Man-in-the-Middle attack. The attack requires the attacker to position themselves in the network path between the vulnerable Perl application and its target HTTPS server. Common scenarios include:

• Compromised or malicious network infrastructure (routers, switches)
• Rogue access points on wireless networks
• DNS spoofing or ARP poisoning attacks
• BGP hijacking for larger-scale attacks

Once positioned, the attacker intercepts the TLS handshake and presents their own certificate. Since HTTP::Tiny does not verify the certificate chain by default, the connection proceeds, allowing the attacker to decrypt all traffic, steal credentials, API keys, session tokens, or inject malicious content into responses.

The vulnerability requires that the attacker achieve a network position enabling interception, which introduces complexity to exploitation. However, in environments such as public WiFi networks, shared hosting, or cloud environments with compromised network components, this attack becomes significantly more feasible.

Detection Methods for CVE-2023-31486

Indicators of Compromise

• Unexpected network traffic patterns or connections to unknown IP addresses from Perl applications
• Certificate warnings or anomalies in downstream logging systems when HTTP::Tiny traffic passes through monitoring proxies
• Presence of HTTP::Tiny usage in codebase without explicit verify_SSL => 1 configuration
• Audit logs showing sensitive data transmissions that may have been intercepted

Detection Strategies

• Conduct code audits to identify HTTP::Tiny instantiations without verify_SSL => 1 parameter
• Deploy network monitoring to detect TLS connections with certificate chain anomalies
• Implement Static Application Security Testing (SAST) rules to flag insecure HTTP::Tiny configurations
• Use dependency scanning tools to identify vulnerable HTTP::Tiny versions in your Perl applications

Monitoring Recommendations

• Enable detailed TLS logging on network security devices to capture certificate validation failures
• Monitor for unusual data exfiltration patterns from Perl-based applications
• Implement certificate transparency log monitoring for domains your applications connect to
• Deploy runtime application monitoring to detect HTTP::Tiny usage patterns in production

How to Mitigate CVE-2023-31486

Immediate Actions Required

• Upgrade HTTP::Tiny to version 0.083 or later where secure defaults are implemented
• Audit all existing code using HTTP::Tiny and add explicit verify_SSL => 1 to all instantiations
• Review CPAN module dependencies for transitive usage of vulnerable HTTP::Tiny versions
• Implement network-level TLS inspection to detect potential MITM attacks in the interim

Patch Information

The vulnerability is addressed in HTTP::Tiny version 0.083 and later. The fix changes the default behavior to verify SSL certificates, aligning with secure-by-default principles. The patch details can be reviewed in the GitHub Pull Request for HTTP::Tiny.

For systems where upgrading is not immediately possible, developers must explicitly enable certificate verification in their code. Additional context and discussion about the vulnerability can be found in the OpenWall OSS Security mailing list and the Hackeriet Blog on Insecure TLS.

Workarounds

• Explicitly set verify_SSL => 1 when creating HTTP::Tiny instances in your Perl applications
• Use alternative HTTP clients like LWP::UserAgent with LWP::Protocol::https that verify certificates by default
• Implement a wrapper function that enforces secure TLS settings across your codebase
• Deploy network-level TLS inspection and certificate pinning where applicable

# Configuration example for secure HTTP::Tiny usage in Perl
# Add verify_SSL => 1 to all HTTP::Tiny instantiations:
# my $http = HTTP::Tiny->new(verify_SSL => 1);

# Verify your HTTP::Tiny version
perl -MHTTP::Tiny -e 'print $HTTP::Tiny::VERSION, "\n"'

# Upgrade HTTP::Tiny via CPAN
cpan HTTP::Tiny

# Or using cpanm
cpanm HTTP::Tiny