CVE-2025-13151 in libtasn1
Summary
by MITRE • 01/08/2026
Stack-based buffer overflow in libtasn1 version: v4.20.0. The function fails to validate the size of input data resulting in a buffer overflow in asn1_expend_octet_string.
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Analysis
by VulDB Data Team • 03/16/2026
The vulnerability identified as CVE-2025-13151 represents a critical stack-based buffer overflow within the libtasn1 library version 4.20.0. This issue stems from inadequate input validation mechanisms within the asn1_expend_octet_string function, which processes ASN.1 encoded data structures commonly used in cryptographic protocols and network communications. The flaw exists in the library's handling of octet string data types, where the function fails to properly check the boundaries of input data before copying it into fixed-size stack buffers. This vulnerability falls under CWE-121 Stack-based Buffer Overflow, a well-documented weakness that allows attackers to overwrite adjacent memory locations and potentially execute arbitrary code. The impact is particularly severe given that libtasn1 is widely used in security-critical applications including GnuPG, GNU TLS, and various cryptographic libraries that rely on ASN.1 encoding for certificate management and secure communications.
The technical exploitation of this vulnerability occurs when an attacker provides maliciously crafted ASN.1 data containing oversized octet strings that exceed the allocated stack buffer size. During processing, the asn1_expend_octet_string function performs a direct copy operation without validating the input length against the buffer boundaries, creating a condition where subsequent stack memory locations become overwritten. This overflow can corrupt return addresses, function pointers, and other critical stack data structures, potentially enabling arbitrary code execution with the privileges of the affected application. The vulnerability aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, as exploitation may involve crafting specific input sequences to trigger the buffer overflow, and T1555.003 Credentials from Password Stores, since compromised applications might access credential storage mechanisms. The attack surface extends to any application or system that utilizes libtasn1 for processing ASN.1 data, including but not limited to email clients, web browsers, and security infrastructure components that handle X.509 certificates and other ASN.1 encoded information.
The operational impact of CVE-2025-13151 extends beyond immediate code execution capabilities to encompass broader system compromise and data integrity threats. Applications leveraging libtasn1 for certificate validation, secure communication protocols, and cryptographic operations become vulnerable to remote exploitation, potentially allowing attackers to impersonate legitimate services, decrypt sensitive communications, or gain unauthorized access to protected resources. The vulnerability's presence in a foundational cryptographic library means that the attack surface is extensive across multiple operating systems and software platforms that depend on libtasn1 for security operations. Organizations using affected versions should consider the potential for privilege escalation attacks, where successful exploitation could lead to complete system compromise, particularly in environments where applications run with elevated privileges. The vulnerability also poses risks to certificate validation processes, potentially enabling man-in-the-middle attacks against secure communications channels that depend on proper ASN.1 parsing. Additionally, the impact extends to network security appliances, firewalls, and intrusion detection systems that utilize libtasn1 for processing security-related ASN.1 data, making this vulnerability particularly dangerous in enterprise and infrastructure security contexts.
Mitigation strategies for CVE-2025-13151 should prioritize immediate patching of affected libtasn1 installations to version 4.20.1 or later, which contains the necessary fixes for the buffer overflow vulnerability. System administrators should implement network segmentation and monitoring to detect potential exploitation attempts, particularly targeting applications that process ASN.1 data from untrusted sources. Input validation should be strengthened at application layers that interface with libtasn1, implementing additional bounds checking and data sanitization measures to prevent malformed ASN.1 data from reaching vulnerable functions. Security teams should consider deploying intrusion detection systems with signature-based detection for known exploitation patterns related to this vulnerability. Organizations should also review their certificate management processes and ensure that applications properly validate certificate chains and handle ASN.1 data with appropriate error handling. The fix implemented in the patched version addresses the root cause by introducing proper input validation and size checking within the asn1_expend_octet_string function, preventing the overflow condition from occurring. Additionally, implementing runtime protections such as stack canaries, address space layout randomization, and control flow integrity checks can provide additional defense-in-depth measures against potential exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify any other applications or systems that may be using vulnerable versions of libtasn1.