CVE-2020-29362: P11-kit Buffer Overflow Vulnerability

CVE-2020-29362 Overview

A heap-based buffer over-read vulnerability has been discovered in p11-kit versions 0.21.1 through 0.23.21. The vulnerability exists in the RPC protocol used by the p11-kit server/remote commands and the client library. When a remote entity supplies a byte array through a serialized PKCS#11 function call, the receiving entity may allow the reading of up to 4 bytes of memory past the heap allocation, potentially leading to information disclosure.

Critical Impact

This vulnerability enables attackers to read up to 4 bytes of memory beyond the intended heap allocation through malicious RPC communications, potentially exposing sensitive information from adjacent memory regions.

Affected Products

• p11-kit versions 0.21.1 through 0.23.21
• Systems using p11-kit server/remote commands
• Applications utilizing the p11-kit client library for PKCS#11 operations

Discovery Timeline

• 2020-12-16 - CVE-2020-29362 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-29362

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read). The flaw resides in the RPC protocol implementation within p11-kit, which is a library that provides a standard configuration setup for PKCS#11 modules. PKCS#11 is a public-key cryptography standard that defines the API for interacting with cryptographic tokens such as smart cards and hardware security modules (HSMs).

The vulnerability occurs during the deserialization of byte arrays transmitted through the RPC protocol. When a remote entity sends a specially crafted byte array as part of a serialized PKCS#11 function call, insufficient bounds checking allows the receiving entity to read beyond the allocated heap buffer by up to 4 bytes. This type of out-of-bounds read can leak sensitive information from adjacent memory regions.

Root Cause

The root cause of this vulnerability is insufficient bounds validation in the RPC protocol handler when processing incoming byte arrays. The code fails to properly verify that the requested read operation stays within the boundaries of the allocated heap buffer, resulting in a heap-based buffer over-read condition. This is a common memory safety issue in C/C++ code where array bounds are not automatically checked.

Attack Vector

The attack is conducted over the network, targeting the RPC protocol used for communication between p11-kit clients and servers. An attacker can exploit this vulnerability by:

1. Establishing a connection to a p11-kit server or interacting with a client library
2. Sending a maliciously crafted serialized PKCS#11 function call containing a specially constructed byte array
3. Triggering the vulnerable code path that reads beyond the heap allocation boundary
4. Potentially extracting sensitive information from adjacent memory regions

The vulnerability exploits the trust relationship in the RPC communication channel, where the receiving entity does not adequately validate the boundaries of incoming data before processing.

Detection Methods for CVE-2020-29362

Indicators of Compromise

• Unusual memory access patterns in p11-kit processes
• Unexpected RPC traffic to p11-kit services with malformed byte array parameters
• Application crashes or abnormal behavior in services using p11-kit
• Memory dump artifacts showing out-of-bounds read attempts

Detection Strategies

• Monitor p11-kit service logs for unusual RPC communication patterns
• Implement memory sanitization tools (AddressSanitizer) in development and testing environments to detect out-of-bounds reads
• Deploy network intrusion detection rules to identify malformed PKCS#11 RPC traffic
• Use runtime application self-protection (RASP) solutions to detect memory access violations

Monitoring Recommendations

• Enable verbose logging for p11-kit services to capture detailed RPC transaction information
• Monitor system memory usage for anomalies that may indicate exploitation attempts
• Implement file integrity monitoring on p11-kit binaries and configuration files
• Review security logs for patterns consistent with information disclosure attacks

How to Mitigate CVE-2020-29362

Immediate Actions Required

• Update p11-kit to version 0.23.22 or later immediately
• Review network access controls to limit exposure of p11-kit RPC services
• Implement network segmentation to isolate systems running vulnerable p11-kit versions
• Audit systems to identify all instances of affected p11-kit versions

Patch Information

Security patches are available for this vulnerability. The p11-kit project has released version 0.23.22 which addresses this heap-based buffer over-read issue. For detailed release information, see the GitHub p11-kit Releases page.

Additional security advisories have been issued:

• GitHub Security Advisory GHSA-5wpq-43j2-6qwc
• Debian Security Advisory DSA-4822
• Debian LTS Announcement January 2021

Workarounds

• Restrict network access to p11-kit RPC services using firewall rules
• Disable remote p11-kit functionality if not required for operations
• Implement network-level access controls to limit RPC communication to trusted hosts only
• Consider using Unix domain sockets instead of network sockets for local-only deployments

# Restrict p11-kit RPC service access via iptables
# Allow only trusted hosts to communicate with p11-kit services
iptables -A INPUT -p tcp --dport 5656 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 5656 -j DROP

# Verify p11-kit version to ensure patched version is installed
pkg-config --modversion p11-kit-1 || p11-kit --version