OESA-2026-2986

cURL is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols.

Security Fix(es):

A use-after-free vulnerability exists in libcurl when an application configures an HTTP/2 stream-dependency tree via CURLOPT_STREAM_DEPENDS or CURLOPT_STREAM_DEPENDS_E, subsequently invokes curl_easy_reset(), and finally terminates the handle with curl_easy_cleanup(). During this final cleanup phase, libcurl attempts to access and modify an internal structure that was already freed during the reset operation.(CVE-2026-10536)

When a user invokes curl using a schemeless URL combined with --proto-default sftp (or scp), a disconnect occurs between the tool layer and libcurl. The tool layer incorrectly infers the URL scheme, which erroneously bypasses the initialization of critical SSH security options like CURLOPTSSHHOSTPUBLICKEYSHA256 and CURLOPTSSHKNOWNHOSTS. Conversely, the libcurl runtime successfully honors CURLOPTDEFAULT_PROTOCOL and establishes the connection via SFTP/SCP as specified. Because the tool layer skipped the security configuration, these SSH host verification options are silently omitted, causing curl to connect to an unverified SSH remote host without throwing an error.(CVE-2026-12064)

A vulnerability exists where a new transfer that uses STARTTLS to upgrade the connection might reuse an existing live connection even though the TLS configuration mismatches so it should not.(CVE-2026-8286)

A flaw in curl’s cookie parsing logic allows a malicious HTTP server to set 'super cookies' that bypass the Public Suffix List check. This enables an attacker-controlled origin to inject cookies that curl subsequently scopes and transmits to unrelated third-party domains.(CVE-2026-8924)

When reusing a libcurl handle for sequential transfers driven by environment-variable proxy configuration, libcurl fails to clear the proxy authentication state between requests. Specifically, if the initial transfer authenticates against proxyA using Digest auth, a subsequent transfer routed through proxyB erroneously leaks the Proxy-Authorization: header intended solely for proxyA.(CVE-2026-8927)

When a libcurl-based application performs transfers via SCP:// or SFTP:// and utilizes the CURLOPT_SSH_KEYFUNCTION callback, it may silently accept an untrusted server. This vulnerability occurs when a server presents a host key type that does not match the specific key type already recorded for that host in the known_hosts file. Instead of rejecting the mismatch, the callback mechanism fails to properly enforce the restriction, allowing the connection to succeed without warning and risking a potential man-in-the-middle attack.(CVE-2026-9547)