OESA-2026-4851

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

Security Fix(es):

When curl is built with GnuTLS, a malicious WebSocket server can make curl send memory past its send buffer. This is due to an out of bounds read following when gnutls_record_send() returns a number of bytes sent greater than the number of bytes it was given to send. GnuTLS does that after a blocked send.(CVE-2026-107928)

Setting CURLOPT_AWS_SIGV4 to NULL but does not disable SigV4 authentication, contrary to expectations and documentation. A subsequent transfer on the same handle still sends an Authorization: AWS4-HMAC-SHA256 header to whatever URL isset next, leaking state information.(CVE-2026-86409)

A flaw in the curl command line tool's logic makes it only set SSH host verification options when interacting directly using SFTP or SCP, and not as a result of following a redirect.(CVE-2026-86410)

An HTTP proxy can trick libcurl into sending the origin's credentials (Basic password, or a Negotiate/Kerberos ticket) to the proxy itself, by answering the CONNECT tunnel request with 401 WWW-Authenticate: instead of the expected 407 Proxy-Authenticate:.(CVE-2026-86414)

Importing a includeSubDomains parent HSTS entry before a longer-lived child entry, silently drops the child. Consequently, when the parent expires, the child's valid HSTS policy is lost, causing curl to issue unencrypted HTTP requests rather than upgrading to HTTPS.(CVE-2026-87862)

An authenticated HTTPS origin can supply an HSTS max-age value that the parser accepts, but time serialization later fails to process. On 64-bit systems, extreme max-age values compute an absolute expiry within standard time integer limits that exceeds calendar time structure bounds. During cache saves, the original HSTS file is truncated before writing a temporary replacement; when serialization fails, the temporary file is deleted, leaving an empty or partial cache. Because the save error is silently ignored during cleanup, curl exits successfully despite the data loss.(CVE-2026-87863)

Enabling CURLOPT_CRLF causes curl to advertise the raw input byte count in the IMAP APPEND {N} literal while transmitting line-ending expanded data. The server reads only $N$ bytes for the payload, causing the remaining overflow bytes to be interpreted and executed as pipelined IMAP commands within the authenticated session.(CVE-2026-87864)

When libcurl uses libssh2 with a hashed known_hosts file, an unrelated initial entry can cause host key validation to report a key mismatch as a missing key to the CURLOPT_SSH_KEYFUNCTION callback.(CVE-2026-87865)

When built with wolfSSL, curl can successfully validate a pinned public key hash against a key the TLS peer does not possess. During the TLS handshake, wolfSSL validates the connection, but curl's subsequent re-parsing of the same certificate - tricked by a manipulated validity length field - extracts and matches a different embedded key, incorrectly authorizing the pinned public key.(CVE-2026-87866)

When writing a long cookie name and value to a Netscape cookie jar, a remote HTTP server can make curl write a record that exceeds its line-length parsing limit. Consequently, any subsequent curl invocation reading from that same cookie jar using --cookie silently aborts parsing prematurely upon encountering the too long line, ignoring all subsequent valid cookies in the file.(CVE-2026-92386)

When an FTP wildcard LIST operation fails, libcurl omits the restoration path meant for successful listings, leaving the write callback set to the internal listing parser and the write callback data pointing directly to the easy handle. Subsequent reuse of this handle triggers an immediate crash, and cloning it via curl_easy_duphandle() copies this corrupted state into the duplicate. If the original handle is subsequently freed, executing a transfer on the cloned handle causes a heap use-after-free read against the dangling handle reference; alternatively, reusing the original or cloned handle while changing only CURLOPT_WRITEDATA (and omitting CURLOPT_WRITEFUNCTION) results in type confusion, forcing the internal parser to interpret incoming server response bytes into memory at the application-supplied write data pointer.(CVE-2026-92388)

libcurl's TFTP state machine fails to validate state transitions against the requested transfer direction, accepting opening server responses for both reads and writes interchangeably. A malicious TFTP server can respond to a download request in a way that forces the client into transmit mode, prompting libcurl to consume and transmit data from the handle's persistent CURLOPT_READDATA pointer - including data remaining from unrelated prior operations, such as an HTTP POST request executed on a reused handle.(CVE-2026-92389)

When invoked with --remote-header-name (-J), curl fails to preserve its documented anti-clobbering protection if an intermediate 103 Early Hints response precedes the final HTTP response, or if an ETag header is processed before Content-Disposition under --etag-save. This flaw allows an HTTP(S) server to overwrite an existing local file specified in the Content-Disposition header despite the presence of the -J non-overwrite constraint.(CVE-2026-92390)

A deeply nested multipart MIME structure constructed via the public API causes a stack overflow in libcurl during normal cleanup operations. An excessive recursion depth within curl_mime_free leads to unbounded stack frame allocation during structure traversal, ultimately crashing the host process.(CVE-2026-92391)

libcurl could accidentally return a URL for curl_easy_getinfo()'s CURLINFO_EFFECTIVE_URL option containing credentials, even though neither the URL provided to libcurl nor the redirected URL did.(CVE-2026-94266)