CVE-1999-0007 in IIS
Summary
by MITRE
Information from SSL-encrypted sessions via PKCS #1.
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Analysis
by VulDB Data Team • 04/17/2026
This vulnerability involves a critical flaw in SSL protocol implementation that allows attackers to extract sensitive information from encrypted sessions through manipulation of PKCS #1 padding schemes. The issue stems from improper handling of cryptographic padding during SSL handshakes where the system fails to adequately validate the integrity of encrypted data structures. When SSL connections utilize PKCS #1 formatted keys or certificates, the vulnerability creates an opportunity for attackers to perform padding oracle attacks that can gradually reveal plaintext information from encrypted communications. The flaw specifically affects implementations that do not properly implement constant-time comparison algorithms for validating PKCS #1 formatted data, making them susceptible to timing-based side-channel attacks that exploit the differences in processing time between valid and invalid padding structures.
The technical implementation of this vulnerability leverages the mathematical properties of RSA encryption and PKCS #1 standard compliance. When SSL servers receive encrypted data that conforms to PKCS #1 specifications, they may inadvertently expose information through error responses or timing variations that occur during decryption processes. This weakness is particularly dangerous in SSL implementations that do not properly sanitize or validate the padding structure of received encrypted payloads. Attackers can systematically test various padding combinations and observe server responses to determine the validity of their guesses, ultimately reconstructing the original plaintext data through statistical analysis and pattern recognition techniques. The vulnerability is classified under CWE-310 as Cryptographic Issues, specifically focusing on improper implementation of cryptographic padding validation mechanisms.
From an operational perspective, this vulnerability can lead to severe consequences including the exposure of sensitive session data, user credentials, and confidential communications that were previously protected by SSL encryption. The impact extends beyond individual session compromises to potentially affect entire SSL infrastructure components, including certificate authorities, web servers, and application servers that rely on PKCS #1 formatted cryptographic operations. Organizations using affected SSL implementations may experience data breaches, regulatory compliance violations, and significant reputational damage when attackers successfully exploit this weakness to extract confidential information from encrypted communications. The vulnerability is particularly concerning because it operates at the cryptographic protocol level, making detection difficult and mitigation complex since it requires changes to core cryptographic implementation details rather than simple configuration updates.
The recommended mitigation strategies involve implementing proper constant-time cryptographic operations for padding validation, upgrading to modern SSL/TLS implementations that do not rely on vulnerable PKCS #1 padding schemes, and ensuring that all cryptographic libraries are properly patched and validated. Security professionals should also consider implementing additional monitoring and detection mechanisms to identify potential exploitation attempts through unusual timing patterns or error response behaviors. Organizations must evaluate their entire cryptographic infrastructure for similar vulnerabilities and ensure compliance with current security standards including those defined in the NIST SP 800-57 cryptographic standards and the OWASP Top Ten security guidelines. The remediation process should include comprehensive testing of cryptographic implementations to verify that padding validation occurs without timing variations that could be exploited by attackers, and that all SSL/TLS implementations properly handle PKCS #1 formatted data according to established security protocols.