CVE-2023-2650: OpenSSL DoS Security Vulnerability

OpenSSL, a globally acknowledged open-source software library for secure communication, has once again found itself in the spotlight, and this time for a less-than-commendable reason. A recently uncovered security vulnerability, tracked as CVE-2023-2650, is causing ripples in the security community. While not the most severe, this moderate vulnerability poses a threat to OpenSSL’s efficient operation by potentially slowing down the processing of certain cryptographic elements.

The issue revolves around ASN.1 (Abstract Syntax Notation One) object identifiers, which in OpenSSL’s realm, are utilized to name and define cryptographic algorithms. These identifiers comprise a series of numbers or sub-identifiers that can be translated from their DER (Distinguished Encoding Rules) form into a canonical numeric text form through the function `OBJ_obj2txt()`. The problem arises when these sub-identifiers are exceedingly large, causing this translation process to become significantly slow, presenting an O(n^2) time complexity.

In the language of the layman, imagine each of these ASN.1 identifiers as a lengthy book, and `OBJ_obj2txt()` as a diligent translator tasked with converting these books into another language. When the books (sub-identifiers) are absurdly lengthy, the translator’s job becomes extremely time-consuming, potentially slowing down the entire library’s operations.

The implications of this vulnerability are more pronounced in specific OpenSSL subsystems such as OCSP, PKCS7/SMIME, CMS, CMP/CRMF, and TS, particularly those operating on OpenSSL 3.0 and newer. Applications directly using `OBJ_obj2txt()` with untrusted data are also at risk. The issue may introduce substantial to prolonged delays while processing messages, potentially leading to a Denial of Service (DoS) scenario.

TLS impact is relatively low due to OpenSSL’s 100KiB limit on the peer’s certificate chain, and this issue primarily impacts clients or servers with explicit client authentication enabled.

For OpenSSL 1.1.1 and 1.0.2, the effects are restricted mainly to displaying various objects, such as X.509 certificates. It’s unlikely to occur in a way that results in a Denial of Service, hence these versions are deemed less affected, and the severity is considered low. Fortunately, no version of the FIPS provider is affected by this issue.

Users of OpenSSL 3.0.x and 3.1.x are susceptible to this vulnerability, and those of OpenSSL 1.1.1 and 1.0.2 may be affected if `OBJ_obj2txt()` is being called directly. It is therefore recommended that users upgrade to the respective patched versions – OpenSSL 3.0.9, OpenSSL 3.1.1, OpenSSL 1.1.1u, and OpenSSL 1.0.2zh (for premium support customers only).

This OpenSSL hiccup was initially detected and reported by OSSfuzz on January 16, 2020. However, it wasn’t identified as a security concern until a reevaluation by Matt Caswell on April 23, 2023. The fix was developed by Richard Levitte.

As we continue to rely on OpenSSL’s cryptographic services, it’s imperative to keep our systems updated, not just to avoid DoS situations like CVE-2023-2650, but to maintain the highest level of security and efficiency.