Heap Buffer Over-read in OpenSSL ASN.1 Decoder

Executive Summary

This vulnerability involves an integer truncation in OpenSSL's ASN.1 decoder when parsing a crafted DER-encoded ASN.1 structure. Specifically, if a primitive element's content length exceeds 2 gigabytes, the length is mishandled, causing the decoder to potentially read beyond the allocated buffer.

On 64-bit Unix and Unix-like platforms, this can lead to a heap buffer over-read, where the application reads memory beyond the intended input buffer. This occurs because the truncated length may cause OpenSSL to scan for a terminating zero byte incorrectly.

Applications using OpenSSL functions like d2i_X509(), d2i_PKCS7(), or other d2i_* decoding functions with attacker-supplied data are affected. However, OpenSSL's own command-line tools are not vulnerable because they check data through the BIO layer before decoding.

This issue only affects 64-bit Unix and Unix-like platforms; 32-bit platforms and 64-bit Windows are not affected. The FIPS modules in OpenSSL versions 3.0 through 4.0 are also not affected.

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Impact Analysis

The heap buffer over-read caused by this vulnerability can lead to application crashes, resulting in Denial of Service (DoS).

Additionally, the vulnerability may cause the decoded ASN.1 object to include memory contents beyond the end of the input buffer, potentially exposing unintended data.

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Compliance Impact

The vulnerability causes a heap buffer over-read that may lead to application crashes (Denial of Service) or reading beyond the intended buffer when parsing ASN.1 structures. However, there is no information provided about any impact on confidentiality, integrity, or availability of sensitive data that would directly relate to compliance with standards such as GDPR or HIPAA.

Since the CVE description and resources do not mention any data breach, unauthorized data access, or leakage, it is unclear how this vulnerability would affect compliance with regulations focused on data protection and privacy.

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Detection Guidance

This vulnerability occurs when parsing a crafted DER-encoded ASN.1 structure with a primitive element whose content exceeds 2 gigabytes in length, causing a heap buffer over-read on 64-bit Unix and Unix-like platforms.

Detection would involve identifying if any applications on your system are passing attacker-supplied data to OpenSSL d2i_* decoding functions such as d2i_X509() or d2i_PKCS7().

Since OpenSSL's own command-line tools are not vulnerable and the issue is specific to 64-bit Unix and Unix-like platforms, detection commands would focus on monitoring or scanning applications that use OpenSSL libraries for ASN.1 decoding.

• Check running processes linked against vulnerable OpenSSL versions.
• Use tools like lsof or netstat to monitor network traffic for suspicious DER-encoded ASN.1 data exceeding 2GB in length.
• Audit application logs for crashes or Denial of Service symptoms related to ASN.1 parsing.

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Mitigation Strategies

Immediate mitigation steps include:

• Avoid processing untrusted or attacker-supplied DER-encoded ASN.1 data with OpenSSL d2i_* decoding functions on affected 64-bit Unix and Unix-like platforms.
• Apply patches or updates from OpenSSL once available that address the integer truncation issue in ASN.1 decoding.
• Monitor applications for abnormal crashes or Denial of Service conditions related to ASN.1 parsing.
• Consider implementing input validation or size checks before passing ASN.1 data to OpenSSL decoding functions.

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