local interface connection reuse mixup

When CURLOPTINTERFACE or the command line tool's --interface option is set with one of the documented prefixes if!, host!, ifhost!, that binding is not part of the connection reuse key, so a later transfer asking for a different source can silently reuse an existing connection and go out from the...

curl_mime_free stack overflow by recursion

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 curlmimefree leads to unbounded stack frame allocation during structure traversal, ultimately crashing the host process...

info leak uploading over WebSockets with GnuTLS

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 gnutlsrecordsend returns a number of bytes sent greater than the number of bytes it was given to send. GnuTLS does that after a blocked...

password leak in CURLINFO_EFFECTIVE_URL

libcurl could accidentally return a URL for curleasygetinfo's CURLINFOEFFECTIVEURL option containing credentials, even though neither the URL provided to libcurl nor the redirected URL did...

Authorization: Negotiate sent to foreign origin

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 t...

TFTP direction confusion

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,...

never-ending loop via server response omission

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...

auto client cert connection reuse mixup

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...

leaking host credentials to HTTP proxy

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:...

wolfSSL public-key pinning bypass

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 -...

FTP connection reuse inherits client-certificate

An ftp:// transfer configured with CURLUSESSLNONE 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...

redirect to SFTP or SCP bypasses host verification

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...

HSTS cache import drops longer-lived child

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...

-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 HTTPS serve...

FTP wildcard write callback mixup

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,...

Negotiate credentials sent to redirected origin

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...

knownhost callback mismatches key as missing

When libcurl uses libssh2 with a hashed knownhosts file, an unrelated initial entry can cause host key validation to report a key mismatch as a missing key to the CURLOPTSSHKEYFUNCTION callback...

server-set cookie erases cookie jar

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 f...

HSTS response erases persisted entries

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...

cross-origin reuse of a Negotiate connection

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...

stale SigV4 headers sent unintended

Setting CURLOPTAWSSIGV4 to NULL 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 is set next, leaking state information...

HTTP/2 upload Use-After-Free

During an upload, curl mishandles HTTP/2 RSTSTREAM received from the server with reason HTTP11REQUIRED or REFUSEDSTREAM leading to a use after free of a struct Curleasy object...

IMAP APPEND plus CRLF conversion command injection

Enabling CURLOPTCRLF 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...

server-set cookie aborts cookie jar load

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...

secure cookie attribute bypass with tab

A Set-Cookie: header using tab horizontal tab, ASCII code 9 instead of space ascii code 32 immediately before the Secure attribute causes curl to store the cookie without its Secure flag. The cookie might then wrongfully be sent over plaintext HTTP on subsequent requests to the same host...

OpenSSL pinning bypass

When CURLOPTPINNEDPUBLICKEY is configured alongside options that disable standard peer verification CURLOPTSSLVERIFYPEER = 0 and CURLOPTSSLVERIFYHOST = 0, libcurl fails to enforce public key pinning on connections established without a presented server certificate. Bypassing the pinning check und...

HTTP/2 server push UAF

A flaw in libcurl's handling of HTTP/2 Server Push streams, when the parent handle is set to share connections with other handles, can lead to use-after-free in the cleanup process...

OpenLDAP SASL authentication bypass

A flaw in the libcurl SASL negotiation for LDAP authentication allows an incomplete handshake sequence to be misinterpreted as a successful cryptographic verification. An attacker executing a Man-in-the-Middle MITM attack can inject a premature or shortcut response that bypasses complete peer...

wolfSSL CA-cache hit overrides callback

With the wolfSSL backend, when CA caching is enabled and an CURLOPTSSLCTXFUNCTION callback replaces the trust store, libcurl can silently reinstall the cached store after the callback returns. A certificate trusted by the cached store but rejected by the callback-selected store is then incorrectl...

domain-scoped PSL domain cookie

When libpsl support is enabled, libcurl fails to enforce the Public Suffix List boundary check when processing a Set-Cookie header where the Domain attribute explicitly matches an origin host that is itself a public suffix e.g., Domain=co.uk set by co.uk. Instead of coercing it into a strict...

native CA store conn reuse

A flaw in libcurl makes it wrongly reuse an existing HTTPS connection setup for a given hostname even when using a different Native CA Store setting CURLSSLOPTNATIVECA than when the connection was created...

OpenSSL provider use-after-free

When performing transfers via libcurl’s multi interface, pooled TLS connections can outlive their originating easy handles. In OpenSSL 3 provider configurations, libcurl attaches an allocated library context to the easy handle's state and passes it to OpenSSL without acquiring an ownership...

Negotiate ambient user conn reuse

A flaw in libcurl makes it wrongly reuse an HTTP connection setup for a given hostname using Negotiate authentication, when the initial request is done using empty credentials. This can make user B's request get sent over user A's previously authenticated connection...

proto-default skips SSH verification

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...

cross-origin Digest auth state leak

Successfully using libcurl to do a transfer to a specific HTTP origin hostA with Digest authentication and then changing the origin to a different one hostB for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Authorization: header field meant for hostA, to hostB...

WS Auto-PONG memory exhaustion

By default, curl automatically responds to WebSocket PING frames. Because curl lacks an upper bound on memory allocation for unacknowledged frames, a malicious server can exhaust all available memory by flooding curl with rapid, sequential PING messages...

QUIC zero-length UDP datagrams busy-loop

An issue in curl’s QUIC UDP receive function allows a malicious HTTP/3 server to trigger a remote denial of service against a curl or libcurl client. Because the helper function discards zero-length UDP datagrams before counting them toward the per-call packet budget, a connected QUIC peer can...

SSH improper host validation

When a libcurl-based application performs transfers via SCP:// or SFTP:// and utilizes the CURLOPTSSHKEYFUNCTION 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 th...

stale proxy password leak

libcurl had a flaw that when instructed to clear proxy authentication credentials which made it not do so, leaving the old credentials around to get used for subsequent transfers that should not know nor use them...

exposing HTTP/3 early data

In this scenario, libcurl first uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate. When libcurl returns to the hostname the second time with a cached SSL...

password leak with netrc and user in URL

When asking curl to use a .netrc file to find credentials and at the same time specifying a URL with a username without a password, like https://[email protected]/, curl could wrongly get and use the password for another user set in the .netrc file for that host if such a one exists and there is n...

trailing dot domain super cookie

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...

wrong reuse for different services

libcurl might in some circumstances reuse the wrong connection when asked to do Negotiate-authenticated ones, even when they are set to use different "services". libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead. When...

Native CA trust persist

libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. An easy handle that first uses default native CA trust can continue trusting the native platform store after the application switches that same handle to custom CA...

sending old referer

A vulnerability in libcurl caused the HTTP Referer: header to persist even when explicitly cleared. While the documentation states that passing NULL to CURLOPTREFERER suppresses the header, the option failed to clear the internal state. As a result, the previous referrer string was erroneously...

HTTP/2 stream-dependency tree UAF

A use-after-free vulnerability exists in libcurl when an application configures an HTTP/2 stream-dependency tree via CURLOPTSTREAMDEPENDS or CURLOPTSTREAMDEPENDSE, subsequently invokes curleasyreset, and finally terminates the handle with curleasycleanup. During this final cleanup phase, libcurl...

UAF after pause in socket callback

Calling curleasypause within the event-based CURLMOPTSOCKETFUNCTION callback triggers a use-after-free vulnerability, where libcurl attempts to store a flag using a dangling struct pointer immediately after that pointer's memory has been freed...

env-set cross-proxy Digest auth state leak

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...

SASL double-free

The curl logic that works with SASL authentication could end up cleaning up the GSASL context twice without clearing the pointer in between, making it free the same pointer twice...

incomplete mTLS config matching in conn reuse

libcurl would reuse a previously created connection even when some mTLS config related option had been changed that should have prohibited reuse. libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. However, some TLS...