The vulnerability indicates that a new transfer which adopts STARTTLS to upgrade the connection can mistakenly reuse an existing live connection even though the TLS configuration mismatches, resulting in the upgrade occurring without the expected security guarantees. This flaw can allow data transmitted after the STARTTLS command to be sent over a channel that does not provide the intended confidentiality and integrity protections. The weakness is classified as CWE‑295.

This issue affects the curl library (libcurl) used by applications that perform STARTTLS operations. No specific version ranges are mentioned, so any build of libcurl that implements STARTTLS could be susceptible. Operators using libcurl should verify the version and look for updates that address this flaw.

The CVSS score of 8.1 indicates high severity, but the EPSS score of less than 1% suggests a low but non‑zero exploitation probability. The vulnerability is not listed in CISA’s KEV catalog. Exploitation would require an attacker to influence the server or network path to trigger a STARTTLS upgrade that reuses a mismatched connection; this scenario is inferred and would likely involve a malicious or misconfigured server or a man‑in‑the‑middle attack. Consequently, the overall risk is moderate, driven largely by the high severity of the potential data compromise.