Affected: curl

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

Affected: Ubuntu:22.04:LTS: curl, Ubuntu:24.04:LTS: curl, Ubuntu:25.10: curl, Ubuntu:26.04:LTS: curl

It was discovered that curl incorrectly reused non-TLS connections when TLS was required in some STARTTLS configurations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-4873)

It was discovered that curl incorrectly reused certain HTTP Negotiate connections. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-5545)

It was discovered that curl incorrectly reused certain SMB connections. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-5773)

It was discovered that curl could leak proxy credentials when handling redirects in some configurations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-6253)

It was discovered that curl could leak cookies because of stale custom cookie host handling in some requests. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-6276)

It was discovered that curl could leak .netrc credentials when reusing proxy connections in some situations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-6429)

It was discovered that curl could leak Digest authentication state when switching proxies in some situations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-7168)