CVE-2022-0778 in Enterprise Session Border Controller
Summary
by MITRE • 03/15/2022
The BN_mod_sqrt() function, which computes a modular square root, contains a bug that can cause it to loop forever for non-prime moduli. Internally this function is used when parsing certificates that contain elliptic curve public keys in compressed form or explicit elliptic curve parameters with a base point encoded in compressed form. It is possible to trigger the infinite loop by crafting a certificate that has invalid explicit curve parameters. Since certificate parsing happens prior to verification of the certificate signature, any process that parses an externally supplied certificate may thus be subject to a denial of service attack. The infinite loop can also be reached when parsing crafted private keys as they can contain explicit elliptic curve parameters. Thus vulnerable situations include: - TLS clients consuming server certificates - TLS servers consuming client certificates - Hosting providers taking certificates or private keys from customers - Certificate authorities parsing certification requests from subscribers - Anything else which parses ASN.1 elliptic curve parameters Also any other applications that use the BN_mod_sqrt() where the attacker can control the parameter values are vulnerable to this DoS issue. In the OpenSSL 1.0.2 version the public key is not parsed during initial parsing of the certificate which makes it slightly harder to trigger the infinite loop. However any operation which requires the public key from the certificate will trigger the infinite loop. In particular the attacker can use a self-signed certificate to trigger the loop during verification of the certificate signature. This issue affects OpenSSL versions 1.0.2, 1.1.1 and 3.0. It was addressed in the releases of 1.1.1n and 3.0.2 on the 15th March 2022. Fixed in OpenSSL 3.0.2 (Affected 3.0.0,3.0.1). Fixed in OpenSSL 1.1.1n (Affected 1.1.1-1.1.1m). Fixed in OpenSSL 1.0.2zd (Affected 1.0.2-1.0.2zc).
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Analysis
by VulDB Data Team • 10/29/2024
The BN_mod_sqrt() function in OpenSSL contains a critical vulnerability that can lead to infinite loops when processing non-prime moduli, creating a denial of service condition that affects multiple cryptographic operations. This flaw exists within the mathematical computation routine responsible for calculating modular square roots, which is fundamental to elliptic curve cryptography operations. The vulnerability specifically manifests when the function encounters elliptic curve parameters that do not meet the mathematical requirements for prime moduli, causing the algorithm to enter an infinite loop rather than properly handling the error condition. This issue is particularly concerning because the function is invoked during the parsing of X.509 certificates that contain elliptic curve public keys in compressed form or explicit elliptic curve parameters with compressed base points, making it accessible through standard certificate processing workflows.
The operational impact of this vulnerability extends across numerous security-sensitive applications and systems that rely on OpenSSL for cryptographic operations. Any process that parses externally supplied certificates or private keys becomes susceptible to this denial of service attack, including TLS clients processing server certificates, TLS servers evaluating client certificates, hosting providers accepting customer certificates or private keys, and certificate authorities parsing certification requests from subscribers. The vulnerability is particularly dangerous because certificate parsing occurs before signature verification, meaning attackers can craft malicious certificates that trigger the infinite loop without requiring valid cryptographic signatures. This allows for remote exploitation against systems that process untrusted certificate data, creating a broad attack surface that spans from web servers to certificate management systems. The issue affects OpenSSL versions 1.0.2, 1.1.1, and 3.0, with specific fixes released in OpenSSL 1.1.1n and 3.0.2 on March 15, 2022, though the vulnerability remained present in versions 3.0.0, 3.0.1, 1.1.1 through 1.1.1m, and 1.0.2 through 1.0.2zc.
The technical implementation of this vulnerability aligns with CWE-835, which describes the weakness of infinite loops or infinite recursion in software systems. From an operational security perspective, this vulnerability maps directly to ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. The flaw represents a classic example of insufficient input validation where the BN_mod_sqrt() function fails to properly validate that the modulus parameter is prime before attempting to compute the square root, resulting in computational exhaustion rather than graceful error handling. The vulnerability can be triggered through multiple vectors including crafted certificates with invalid explicit curve parameters, private keys containing malicious elliptic curve data, and self-signed certificates that force signature verification to occur after the initial parsing phase. While OpenSSL 1.0.2 was slightly more resistant due to delayed public key parsing, all versions remain vulnerable when cryptographic operations requiring the public key are performed, making the mitigation strategy crucial for all affected deployments. The fix implemented in the patched versions ensures that the BN_mod_sqrt() function properly validates input parameters and terminates execution appropriately when encountering invalid mathematical conditions rather than entering infinite computational loops.