CVE-2020-29361: P11-kit Buffer Overflow Vulnerability

CVE-2020-29361 Overview

An integer overflow vulnerability was discovered in p11-kit versions 0.21.1 through 0.23.21. Multiple integer overflows exist in the array allocations within the p11-kit library and the p11-kit list command. The vulnerability occurs because overflow checks are missing before calling realloc or calloc memory allocation functions. This flaw can be exploited remotely to cause denial of service conditions affecting systems that rely on p11-kit for PKCS#11 module management.

Critical Impact

Remote attackers can trigger integer overflows in memory allocation routines, potentially causing application crashes and denial of service on systems using p11-kit for cryptographic token management.

Affected Products

• p11-kit versions 0.21.1 through 0.23.21
• Debian Linux 9.0
• Debian Linux 10.0

Discovery Timeline

• 2020-12-16 - CVE CVE-2020-29361 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-29361

Vulnerability Analysis

This vulnerability is classified as CWE-190 (Integer Overflow or Wraparound). The p11-kit library, which provides a way to load and enumerate PKCS#11 modules, contains multiple locations where array allocations are performed without proper overflow validation. When processing module lists or performing array operations, the library calculates buffer sizes by multiplying element counts with element sizes. Without proper bounds checking, these calculations can overflow, resulting in undersized buffer allocations.

When an attacker can influence the input that determines array sizes, they can craft inputs that cause the multiplication to wrap around, leading to a much smaller allocation than expected. Subsequent operations then write beyond the allocated buffer boundaries, causing memory corruption and application crashes.

Root Cause

The root cause is missing integer overflow validation in array allocation code paths within the p11-kit library. Specifically, when the library performs calculations like count * sizeof(element) before calling realloc or calloc, it fails to verify that the multiplication result does not exceed the maximum representable value. This allows attackers to trigger wraparound conditions where the resulting allocation size is significantly smaller than required.

Attack Vector

The vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can send specially crafted data to applications using the p11-kit library, triggering the integer overflow condition in memory allocation routines. The attack primarily leads to denial of service through application crashes, as the resulting heap corruption disrupts normal memory management operations.

The exploitation process involves supplying large values that, when multiplied, overflow to produce small allocation sizes. When the application attempts to populate these undersized buffers with the expected amount of data, heap corruption occurs, leading to crashes or potentially more severe memory safety violations.

Detection Methods for CVE-2020-29361

Indicators of Compromise

• Unexpected crashes in applications using p11-kit library with heap corruption errors
• Segmentation faults or memory access violations in processes linked against libp11-kit
• Abnormal memory allocation patterns in system logs for PKCS#11-related services
• Core dumps indicating memory corruption in p11-kit library functions

Detection Strategies

• Monitor for crash reports in applications that link against p11-kit, particularly those involving heap corruption
• Implement runtime memory sanitizers (ASan, MSan) in development and testing environments to detect overflow conditions
• Deploy endpoint detection solutions capable of identifying memory corruption exploitation attempts
• Review system logs for unusual patterns in applications interfacing with PKCS#11 modules

Monitoring Recommendations

• Enable detailed logging for applications using p11-kit to capture allocation-related errors
• Configure system monitors to alert on repeated application crashes involving p11-kit
• Deploy intrusion detection signatures for unusual PKCS#11 module enumeration patterns
• Monitor network traffic for anomalous data volumes targeting services that use p11-kit

How to Mitigate CVE-2020-29361

Immediate Actions Required

• Update p11-kit to version 0.23.22 or later, which includes fixes for the integer overflow vulnerabilities
• Apply vendor-specific patches for affected Linux distributions (Debian DSA-4822)
• Restart applications and services that link against p11-kit after applying updates
• Prioritize patching on systems where p11-kit is exposed to untrusted network input

Patch Information

The p11-kit project has released security updates addressing this vulnerability. Refer to the GitHub p11-kit Releases page for the latest patched versions. The GitHub Security Advisory GHSA-q4r3-hm6m-mvc2 provides detailed information about the vulnerability and remediation.

For Debian systems, security updates are available through Debian Security Advisory DSA-4822 and the Debian LTS Announcement.

Workarounds

• Limit network exposure of services using p11-kit to trusted networks only
• Implement input validation at the application level before passing data to p11-kit functions
• Consider using application sandboxing to limit the impact of potential exploitation
• Deploy network-level filtering to restrict access to services utilizing PKCS#11 functionality

# Example: Update p11-kit on Debian-based systems
sudo apt-get update
sudo apt-get install --only-upgrade p11-kit libp11-kit0

# Verify installed version is 0.23.22 or later
dpkg -l | grep p11-kit