When processing an HTTP redirect to a URL containing userinfo (a
`username:password` component), curl might erroneously retain and re-transmit
the original host's HTTP Negotiate authentication state. Consequently, a
malicious server can trigger a redirect containing arbitrary userinfo to force
curl to send a freshly minted Kerberos ticket—generated using the ambient
identity of the client process to an untrusted third-party host, effectively
bypassing the domain-scoping restrictions normally enforced by the absence of
`--location-trusted`.
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.
-J no-clobber guarantee bypassed with 103 early hints
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.
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.
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
By permanently omitting the final control-response line, a malicious FTP,
IMAP, POP3, or SMTP server can exploit libcurl and completely bypass its
configured transfer timeout mechanism, indefinitely blocking all concurrent
transfers bound to the same multi-handle.
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.
When using an *ambient user* in a first transfer doing Negotiate
authentication and asked to follow redirects, curl could pass on its
credential details to an unrelated second origin when asked to redirect there.
A remote HTTP server can set a cookie that curl accepts and writes to a
Netscape cookie jar but cannot reload. On the next invocation using the same
path for `--cookie` and `--cookie-jar`, curl fails before connecting, then the
cleanup procedure replaces the jar with an empty file, deleting cookies for
unrelated domains.
An `ftp://` transfer configured with `CURLUSESSL_NONE` can reuse a pooled FTP
control connection that a previous easy handle upgraded with `STARTTLS` and
authenticated using a client certificate. The second handle performs neither a
new TLS handshake nor a new FTP login, so the server continues to authorize it
under the first handle's certificate identity.
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.
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.
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.
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.
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.
IMAP APPEND plus CRLF conversion command injection
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.
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.
When using ambient user credentials, an HTTP request directed to one origin
may be dispatched over a connection previously authenticated via Negotiate for
a different origin, leaving the request's intended credentials unused.
libcurl's connection cache match function never considers the automatic client
certificate option, so a cached, already authenticated Schannel connection can
be handed to a transfer that got redirected to a different origin, even though
the code explicitly switched off the auto client cert option for that transfer
to prevent exactly this.
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:`.