CVE-2025-52497: Arm Mbed TLS Buffer Overflow Vulnerability

CVE-2025-52497 Overview

CVE-2025-52497 is a heap-based buffer underflow vulnerability affecting Mbed TLS versions prior to 3.6.4. The flaw exists in PEM parsing functionality, specifically within the mbedtls_pem_read_buffer function and two mbedtls_pk_parse functions. Attackers can exploit this vulnerability by providing specially crafted, untrusted PEM input, potentially leading to information disclosure or denial of service conditions.

Critical Impact

This buffer underflow vulnerability in Mbed TLS's PEM parsing routines could allow network-based attackers to trigger memory corruption through malicious PEM input, potentially causing application crashes or leaking sensitive memory contents.

Affected Products

• Arm Mbed TLS versions prior to 3.6.4
• Systems and applications using vulnerable Mbed TLS libraries for PEM parsing
• IoT devices and embedded systems implementing Mbed TLS cryptographic operations

Discovery Timeline

• 2025-07-04 - CVE-2025-52497 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-52497

Vulnerability Analysis

This vulnerability is classified as CWE-193 (Off-by-one Error), manifesting as a one-byte heap-based buffer underflow during PEM parsing operations. The flaw affects core cryptographic parsing functions in Mbed TLS, which is widely deployed in embedded systems, IoT devices, and applications requiring lightweight TLS/SSL implementations.

The vulnerability can be triggered remotely without authentication or user interaction, though exploitation requires specific conditions to be met, making it moderately complex to exploit. Successful exploitation could result in limited confidentiality impact through memory disclosure and limited availability impact through potential application crashes.

Root Cause

The root cause is an off-by-one error (CWE-193) in the PEM parsing implementation. When processing PEM-encoded data, the affected functions (mbedtls_pem_read_buffer and the two mbedtls_pk_parse functions) incorrectly calculate buffer boundaries, resulting in a one-byte underflow condition on the heap. This occurs when parsing untrusted PEM input that has been specially crafted to trigger the boundary calculation error.

Attack Vector

The attack vector is network-based, allowing remote attackers to exploit this vulnerability by supplying malicious PEM-encoded data to applications using vulnerable Mbed TLS versions. The attack does not require authentication or user interaction. However, the high attack complexity indicates that specific preconditions must be met for successful exploitation, such as the target application accepting and parsing untrusted PEM input.

The vulnerability affects scenarios where:

• Applications parse PEM certificates or keys from untrusted sources
• TLS/SSL connections accept PEM-encoded data during handshakes
• IoT devices process externally supplied cryptographic material

For detailed technical analysis, refer to the GitHub Mbed TLS Security Advisory.

Detection Methods for CVE-2025-52497

Indicators of Compromise

• Unexpected application crashes in processes using Mbed TLS PEM parsing functions
• Memory corruption errors or segmentation faults when processing PEM-encoded data
• Anomalous heap memory access patterns detected by memory debugging tools
• Application logs indicating parsing failures for PEM certificates or keys

Detection Strategies

• Deploy memory sanitizers (AddressSanitizer, Valgrind) in development and testing environments to detect buffer underflow conditions
• Monitor applications using Mbed TLS for unexpected crashes or restarts that may indicate exploitation attempts
• Implement input validation logging to track malformed PEM data submissions
• Use SentinelOne's behavioral AI to detect anomalous memory access patterns in processes handling cryptographic operations

Monitoring Recommendations

• Enable detailed logging for applications processing PEM-encoded certificates and keys
• Monitor system health metrics for applications using Mbed TLS libraries for signs of instability
• Configure alerting for repeated PEM parsing failures which may indicate probing or exploitation attempts
• Review application dependencies to identify all instances of vulnerable Mbed TLS versions across the environment

How to Mitigate CVE-2025-52497

Immediate Actions Required

• Upgrade Mbed TLS to version 3.6.4 or later across all affected systems immediately
• Conduct an inventory of all applications and devices using Mbed TLS to identify vulnerable deployments
• Implement input validation to reject malformed or suspicious PEM-encoded data before parsing
• Consider isolating or restricting network access to systems that cannot be immediately patched

Patch Information

The vulnerability has been addressed in Mbed TLS version 3.6.4. Organizations should update their Mbed TLS installations to this version or later to remediate the vulnerability. For detailed patch information, consult the GitHub Mbed TLS Security Advisory. Debian users should also review the Debian LTS Announcement for distribution-specific patches.

Workarounds

• Restrict PEM parsing to trusted input sources only where possible
• Implement application-level input validation to reject oversized or malformed PEM data
• Deploy network-level filtering to inspect and sanitize PEM-encoded content before it reaches vulnerable applications
• Use runtime application self-protection (RASP) or memory safety tools as an additional defense layer

# Example: Updating Mbed TLS on Debian-based systems
sudo apt update
sudo apt install libmbedtls-dev=3.6.4-1
# Verify installed version
apt-cache policy libmbedtls-dev