CVE-2023-52892 in phpseclib
Summary
by MITRE • 06/28/2024
In phpseclib before 1.0.22, 2.x before 2.0.46, and 3.x before 3.0.33, some characters in Subject Alternative Name fields in TLS certificates are incorrectly allowed to have a special meaning in regular expressions (such as a + wildcard), leading to name confusion in X.509 certificate host verification.
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Analysis
by VulDB Data Team • 02/08/2025
The vulnerability identified as CVE-2023-52892 represents a critical security flaw in the phpseclib library that affects multiple versions across its 1.x, 2.x, and 3.x release lines. This issue stems from improper handling of Subject Alternative Name (SAN) fields within X.509 TLS certificates during host verification processes. The flaw allows certain characters that should be treated as literal values to be interpreted as regular expression metacharacters, creating potential for certificate forgery and man-in-the-middle attacks. The vulnerability specifically impacts the library's ability to properly validate certificate hostnames, which is fundamental to establishing secure communications in web applications and services that rely on phpseclib for cryptographic operations.
The technical root cause of this vulnerability lies in the library's insufficient sanitization of characters within the Subject Alternative Name fields of TLS certificates. When phpseclib processes certificate verification, it incorrectly interprets certain special characters such as the plus symbol as regular expression wildcards rather than literal characters. This misinterpretation occurs during the hostname matching process where the library should strictly validate that the certificate's subject alternative names match the expected hostnames. The improper handling creates a path where an attacker could potentially craft a certificate containing special characters that would bypass validation checks, allowing a malicious certificate to appear valid when it should be rejected. This flaw directly violates the principles of secure certificate validation and undermines the trust model that TLS certificates are designed to establish.
The operational impact of CVE-2023-52892 extends far beyond simple certificate validation failures, as it fundamentally compromises the security of any application relying on phpseclib for secure communications. Systems using affected versions of the library become vulnerable to certificate confusion attacks where malicious actors can exploit the regular expression interpretation flaw to bypass hostname verification. This vulnerability is particularly dangerous in environments where applications establish secure connections to remote services, perform SSH operations, or handle encrypted communications, as it could allow attackers to intercept and manipulate traffic between clients and servers. The attack surface is broad given phpseclib's widespread adoption in web applications, content management systems, and various PHP-based services that require secure cryptographic operations.
Organizations should immediately implement mitigations by upgrading to the patched versions of phpseclib, specifically versions 1.0.22, 2.0.46, and 3.0.33 respectively for each affected branch. The vulnerability aligns with CWE-1107, which addresses improper neutralization of special elements used in regular expressions, and represents a clear violation of secure coding practices in cryptographic libraries. Security teams should also consider implementing additional monitoring for certificate validation failures and network traffic anomalies that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1552.001, which covers "Unsecured Credentials" and "Credential Access" techniques, as compromised certificate validation can lead to unauthorized access through credential interception. Organizations should conduct comprehensive vulnerability assessments to identify all systems using affected phpseclib versions and ensure proper patch management procedures are in place to prevent future occurrences of similar issues.