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...

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...

Credential leak on redirect

curl follows HTTPS redirects when asked to. curl also supports authentication. When a user and password are provided for a URL with a given hostname, curl makes an effort to not pass on those credentials to other hosts in redirects unless given permission with a special option. This "same host...

connection reuse ignores TLS requirement

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 transm...

OCSP stapling bypass with GnuTLS

When curl is told to use the Certificate Status Request TLS extension, often referred to as OCSP stapling, to verify that the server certificate is valid, it might fail to detect some OCSP problems and instead wrongly consider the response as fine. If the returned status reports another error tha...

TLS certificate check bypass with mbedTLS/PolarSSL

libcurl did not check the server certificate of TLS connections done to a host specified as an IP address, or when explicitly asked to use SSLv3. This flaw only exists when libcurl is built to use mbedTLS or PolarSSL as the TLS backend. The documentation for mbedTLS and PolarSSL wrongly says that...

URL request injection

When libcurl sends a request to a server via an HTTP proxy, it copies the entire URL into the request and sends if off. If the given URL contains line feeds and carriage returns those are sent along to the proxy too, which allows the program to for example send a separate HTTP request injected...

bearer token leak on cross-protocol redirect

When an OAuth2 bearer token is used for an HTTPS transfer, and that transfer performs a cross-protocol redirect to a second URL that uses an IMAP, LDAP, POP3 or SMTP scheme, curl might wrongly pass on the bearer token to the new target host...

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...

stale custom cookie host causes cookie leak

Using libcurl, when a custom Host: header is first set for an HTTP request and a second request is subsequently done using the same easy handle but without the custom Host: header set, the second request would use stale information and pass on cookies meant for the first host in the second reques...

HSTS bypass via IDN

curl's HSTS check could be bypassed to trick it to keep using HTTP. Using its HSTS support, curl can be instructed to use HTTPS directly instead of using an insecure clear-text HTTP step even when HTTP is provided in the URL. This mechanism could be bypassed if the hostname in the given URL uses...

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...

cross-proxy Digest auth state leak

Successfully using libcurl to do a transfer over a specific HTTP proxy proxyA with Digest authentication and then changing the proxy host to a second one proxyB for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Proxy-Authorization: header field meant for proxyA, to...

netrc and default credential leak

When asked to use a .netrc file for credentials and to follow HTTP redirects, curl could leak the password used for the first host to the followed-to host under certain circumstances. This flaw only manifests itself if the netrc file has a default entry that omits both login and password. A rare...

HTTP/2 trailer out-of-bounds read

libcurl contains an out bounds read in code handling HTTP/2 trailers. It was reported that reading an HTTP/2 trailer could mess up future trailers since the stored size was one byte less than required. The problem is that the code that creates HTTP/1-like headers from the HTTP/2 trailer data once...

HTTP authentication leak in redirects

curl might leak authentication data to third parties. When asked to send custom headers in its HTTP requests, curl sends that set of headers first to the host in the initial URL but also, if asked to follow redirects and a 30X HTTP response code is returned, to the host mentioned in URL in the...

IP address wildcard certificate validation

libcurl incorrectly validates wildcard SSL certificates containing literal IP addresses. RFC 2818 covers the requirements for matching Common Names CNs and subjectAltNames in order to establish valid SSL connections. It first discusses CNs that are for hostnames, and the rules for wildcards in 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...

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...

OCSP stapling bypass with Apple SecTrust

When curl is told to use the Certificate Status Request TLS extension, often referred to as OCSP stapling, to verify that the server certificate is valid, it fails to detect OCSP problems and instead wrongly consider the response as fine...

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...

Reusing connections with wrong client cert

libcurl did not consider client certificates when reusing TLS connections. libcurl supports reuse of established connections for subsequent requests. It does this by keeping a few previous connections "alive" in a connection pool so that a subsequent request that can use one of them instead of...

wrong proxy connection reuse with credentials

curl would wrongly reuse an existing HTTP proxy connection doing CONNECT to a server, even if the new request uses different credentials for the HTTP proxy. The proper behavior is to create or use a separate connection...

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...

wrong reuse of HTTP Negotiate connection

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTPS request after a Negotiate-authenticated one, when both use the same host. libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid...

RTSP RTP buffer over-read

curl can be tricked into copying data beyond end of its heap based buffer. When asked to transfer an RTSP URL, curl could calculate a wrong data length to copy from the read buffer. The memcpy call would copy data from the heap following the buffer to a storage area that would subsequently be...

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...

netrc credential leak with reused proxy connection

When asked to both use a .netrc file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances...

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...

UAF and double free in MQTT sending

When sending data to an MQTT server, libcurl could in some circumstances erroneously keep a pointer to an already freed memory area and both use that again in a subsequent call to send data and also free it again...

TLS session resumption client cert bypass (again)

libcurl would attempt to resume a TLS session even if the client certificate had changed. That is unacceptable since a server by specification is allowed to skip the client certificate check on resume, and may instead use the old identity which was established by the previous certificate or no...

FTP Server Response Buffer Overflow

When storing an FTP server's error message on failure, there was no check for input length and thus a malicious FTP server could overflow curl's stack based buffer...

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...

TLS session resumption client cert bypass

libcurl would attempt to resume a TLS session even if the client certificate had changed. That is unacceptable since a server by specification is allowed to skip the client certificate check on resume, and may instead use the old identity which was established by the previous certificate or no...

Authentication Buffer Overflows

Due to bad usage of the base64 decode function to a stack-based buffer without checking the data length, it was possible for a malicious HTTP server to overflow the client during NTLM negotiation and for an FTP server to overflow the client during krb4 negotiation. The announcement of this flaw w...

bad reuse of HTTP Negotiate connection

libcurl can in some circumstances reuse the wrong connection when asked to do an Negotiate-authenticated HTTP or HTTPS request. libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead. When reusing a connection a range of...

token leak with redirect and netrc

When an OAuth2 bearer token is used for an HTTPS transfer, and that transfer performs a redirect to a second URL, curl could leak that token to the second hostname under some circumstances. If the hostname that the first request is redirected to has information in the used .netrc file, with eithe...

SOCKS5 heap buffer overflow

This flaw makes curl overflow a heap based buffer in the SOCKS5 proxy handshake. When curl is asked to pass along the hostname to the SOCKS5 proxy to allow that to resolve the address instead of it getting done by curl itself, the maximum length that hostname can be is 255 bytes. If the hostname ...

duphandle read out of bounds

libcurl's function curleasyduphandle has a bug that can lead to libcurl eventually sending off sensitive data that was not intended for sending. When doing an HTTP POST transfer with libcurl, you can use the CURLOPTCOPYPOSTFIELDS option to specify a memory area holding the data to send to the...

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...

libssh key passphrase bypass without agent set

When doing SSH-based transfers using either SCP or SFTP, and asked to do public key authentication, curl would wrongly still ask and authenticate using a locally running SSH agent...

No QUIC certificate pinning with wolfSSL

libcurl supports pinning of the server certificate public key for HTTPS transfers. Due to an omission, this check is not performed when connecting with QUIC for HTTP/3, when the TLS backend is wolfSSL. Documentation says the option works with wolfSSL, failing to specify that it does not for QUIC...

curl overwrite local file with -J

curl can be tricked by a malicious server to overwrite a local file when using -J --remote-header-name and -i --include in the same command line. The command line tool offers the -J option that saves a remote file using the filename present in the Content-Disposition: response header. curl then...

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...

IDN wildcard match

curl supports matching of wildcard patterns when listed as "Subject Alternative Name" in TLS server certificates. curl can be built to use its own name matching function for TLS rather than one provided by a TLS library. This private wildcard matching function would match IDN International Domain...

CURLOPT_SSLCERT mix-up with Secure Transport

libcurl-using applications can ask for a specific client certificate to be used in a transfer. This is done with the CURLOPTSSLCERT option --cert with the command line tool. When libcurl is built to use the macOS native TLS library Secure Transport, an application can ask for the client certifica...

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 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...

broken TLS options for threaded LDAPS

When doing multi-threaded LDAPS transfers LDAP over TLS with libcurl, changing TLS options in one thread would inadvertently change them globally and therefore possibly also affect other concurrently setup transfers. Disabling certificate verification for a specific transfer could unintentionally...

Proxy Authentication Header Information Leakage

When curl connected to a site via an HTTP proxy with the CONNECT request, the user and password used for the proxy connection was also sent off to the remote server...