CVE-2021-22924 is a vulnerability in libcurl, a widely used client-side URL transfer library, affecting versions from 7.10.4 up to and including 7.77.0. The issue arises from improper input validation related to connection reuse in libcurl's connection pooling mechanism. libcurl maintains a pool of previously used connections to optimize subsequent transfers by reusing connections that match the current setup. However, the logic responsible for matching configurations failed to consider the 'issuercert' parameter and performed file path comparisons in a case-insensitive manner. This is problematic because file paths can be case-sensitive depending on the operating system and file system used. Additionally, the omission of the 'issuer cert' in the comparison means that libcurl might incorrectly reuse a connection intended for a different server certificate verification context. This flaw could lead to libcurl reusing an incorrect connection, potentially causing data to be sent over an unintended connection or to an unintended server. The vulnerability is classified under CWE-20 (Improper Input Validation). The CVSS v3.1 base score is 3.7 (low severity), reflecting a network attack vector but requiring high attack complexity, no privileges, and no user interaction, with limited confidentiality impact and no integrity or availability impact. There are no known exploits in the wild, and no official patches were linked in the provided data, though later libcurl versions have addressed this issue. The vulnerability primarily affects applications and systems that rely on vulnerable libcurl versions for secure communications, especially where issuer certificate validation is critical.

For European organizations, the impact of CVE-2021-22924 is generally low but context-dependent. Organizations using libcurl versions up to 7.77.0 in environments where secure HTTPS connections and certificate validation are critical could face risks of misrouted or improperly validated connections. This could potentially lead to minor confidentiality issues, such as data leakage or exposure to man-in-the-middle scenarios if connections are reused incorrectly. However, the vulnerability does not affect integrity or availability directly and requires a high attack complexity, reducing the likelihood of exploitation. European sectors with stringent data protection requirements, such as finance, healthcare, and government, might be more sensitive to any confidentiality lapses. Additionally, organizations deploying libcurl in large-scale or automated environments where connection reuse is frequent might experience subtle security risks. Overall, while the direct impact is limited, the vulnerability underscores the importance of correct certificate validation and connection management in secure communications.

To mitigate CVE-2021-22924, European organizations should: 1) Upgrade libcurl to versions later than 7.77.0 where this vulnerability has been fixed, ensuring the connection matching logic properly considers 'issuercert' and performs case-sensitive path comparisons where appropriate. 2) Audit and inventory all software and services using libcurl to identify vulnerable versions, including embedded devices and third-party applications. 3) Where immediate upgrades are not feasible, implement network-level controls such as strict TLS inspection and monitoring to detect anomalous connection reuse or certificate mismatches. 4) Enforce strict certificate pinning or validation policies in applications using libcurl to reduce reliance on connection reuse logic. 5) Conduct security testing and code reviews focusing on connection reuse and certificate validation mechanisms to identify similar logic flaws. 6) Educate developers and system administrators about the risks of improper input validation and the importance of keeping third-party libraries up to date.