CURL-CVE-2022-30115 HSTS bypass via trailing dot

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 used ...

CURL-CVE-2022-22576 OAUTH2 bearer bypass in connection reuse

libcurl might reuse OAUTH2-authenticated connections without properly making sure that the connection was authenticated with the same credentials as set for this transfer. This affects SASL-enabled protocols: SMTPS, IMAPS, POP3S and LDAPS OpenLDAP only. libcurl maintains a pool of live connection...

CURL-CVE-2018-1000122 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...

CURL-CVE-2016-8620 glob parser write/read out of bounds

The curl tool's "globbing" feature allows a user to specify a numerical range through which curl iterates. It is typically specified as 1-5, specifying the first and the last numbers in the range. Or with a-z, using letters. 1. The curl code for parsing the second unsigned number did not check fo...

CURL-CVE-2016-5421 use of connection struct after free

libcurl is vulnerable to a use after free flaw. libcurl works with easy handles using the type 'CURL ' that are objects the application creates using curleasyinit. They are the handles that are all each associated with a single transfer at a time. libcurl also has an internal struct that represen...

CURL-CVE-2016-5419 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...

CURL-CVE-2015-3148 Negotiate not treated as connection-oriented

libcurl keeps a pool of its last few connections around after use to facilitate easy, convenient and completely transparent connection reuse for applications. When doing HTTP requests Negotiate authenticated, the entire connection may become authenticated and not only the specific HTTP request...

CURL-CVE-2014-8151 Secure Transport certificate check bypass

libcurl stores TLS Session IDs in its associated Session ID cache when it connects to TLS servers. In subsequent connects it reuses the entry in the cache to resume the TLS connection faster than when doing a full TLS handshake. The actual implementation for the Session ID caching varies dependin...

CURL-CVE-2025-4947 QUIC certificate check skip with wolfSSL

libcurl accidentally skips the certificate verification for QUIC connections when connecting to a host specified as an IP address in the URL. Therefore, it does not detect impostors or man-in-the-middle attacks...

CURL-CVE-2021-22946 Protocol downgrade required TLS bypassed

A user can tell curl to require a successful upgrade to TLS when speaking to an IMAP, POP3 or FTP server --ssl-reqd on the command line or CURLOPTUSESSL set to CURLUSESSLCONTROL or CURLUSESSLALL with libcurl. This requirement could be bypassed if the server would return a properly crafted but...

CURL-CVE-2020-8286 Inferior OCSP verification

libcurl offers "OCSP stapling" via the CURLOPTSSLVERIFYSTATUS option. When set, libcurl verifies the OCSP response that a server responds with as part of the TLS handshake. It then aborts the TLS negotiation if something is wrong with the response. The same feature can be enabled with --cert-stat...

CURL-CVE-2020-8231 wrong connect-only connection

An application that performs multiple requests with libcurl's multi API and sets the CURLOPTCONNECTONLY option, might in rare circumstances experience that when subsequently using the setup connect-only transfer, libcurl picks and uses the wrong connection - and instead picks another one the...

CURL-CVE-2018-1000121 LDAP NULL pointer dereference

curl might dereference a near-NULL address when getting an LDAP URL. The function ldapgetattributeber is called to get attributes, but it turns out that it can return LDAPSUCCESS and still return a NULL pointer in the result pointer when getting a particularly crafted response. This was a surpris...

CURL-CVE-2017-1000100 TFTP sends more than buffer size

When doing a TFTP transfer and curl/libcurl is given a URL that contains a long filename longer than about 515 bytes, the filename is truncated to fit within the buffer boundaries, but the buffer size is still wrongly updated to use the original length. This too large value is then used in the...

CURL-CVE-2016-8618 double free in curl_maprintf

The libcurl API function called curlmaprintf can be tricked into doing a double free due to an unsafe sizet multiplication, on systems using 32-bit sizet variables. The function is also used internally in numerous situations. The function doubles an allocated memory area with realloc and allows t...

CURL-CVE-2016-7167 curl escape and unescape integer overflows

The four libcurl functions curlescape, curleasyescape, curlunescape and curleasyunescape perform string URL percent escaping and unescaping. They accept custom string length inputs in signed integer arguments. The functions having names without "easy" being the deprecated versions of the others...

CURL-CVE-2016-7141 Incorrect reuse of client certificates

libcurl built on top of NSS Network Security Services incorrectly reused client certificates if a certificate from file was used for one TLS connection but no certificate set for a subsequent TLS connection. While the symptoms are similar to CVE-2016-5420 Reusing connection with wrong client cert...

CURL-CVE-2016-5420 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...

CURL-CVE-2015-3237 SMB send off unrelated memory contents

libcurl can get tricked by a malicious SMB server to send off data it did not intend to. In libcurl's state machine function handling the SMB protocol smbrequeststate, two length and offset values are extracted from data that has arrived over the network, and those values are subsequently used to...

CURL-CVE-2014-3613 cookie leak with IP address as domain

By not detecting and rejecting domain names for partial literal IP addresses properly when parsing received HTTP cookies, libcurl can be fooled to both sending cookies to wrong sites and into allowing arbitrary sites to set cookies for others. For this problem to trigger, the client application...

CURL-CVE-2026-82209 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...

CURL-CVE-2026-80229 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...

CURL-CVE-2026-19931 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...

CURL-CVE-2026-3784 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...

CURL-CVE-2022-32208 FTP-KRB bad message verification

When curl does FTP transfers secured by krb5, it handles message verification failures wrongly. This flaw makes it possible for a Man-In-The-Middle attack to go unnoticed and even allows it to inject data to the client...

CURL-CVE-2022-27779 cookie for trailing dot TLD

libcurl wrongly allows HTTP cookies to be set for Top Level Domains TLDs if the hostname is provided with a trailing dot. curl can be told to receive and send cookies when communicating using HTTPS. curl's "cookie engine" can be built with or without Public Suffix List awareness. If PSL support n...

CURL-CVE-2021-22947 STARTTLS protocol injection via MITM

When curl connects to an IMAP, POP3, SMTP or FTP server to exchange data securely using STARTTLS to upgrade the connection to TLS level, the server can still respond and send back multiple responses before the TLS upgrade. Such multiple pipelined responses are cached by curl. curl would then...

CURL-CVE-2021-22897 Schannel cipher selection surprise

libcurl lets applications specify which specific TLS ciphers to use in transfers, using the option called CURLOPTSSLCIPHERLIST. The cipher selection is used for the TLS negotiation when a transfer is done involving any of the TLS based transfer protocols libcurl supports, such as HTTPS, FTPS,...

CURL-CVE-2019-5481 FTP-KRB double free

libcurl can be told to use kerberos over FTP to a server, as set with the CURLOPTKRBLEVEL option. During such kerberos FTP data transfer, the server sends data to curl in blocks with the 32-bit size of each block first and then that amount of data immediately following. A malicious or broken serv...

CURL-CVE-2017-8817 FTP wildcard out of bounds read

libcurl contains a read out of bounds flaw in the FTP wildcard function. libcurl's FTP wildcard matching feature, which is enabled with the CURLOPTWILDCARDMATCH option can use a built-in wildcard function or a user provided one. The built-in wildcard function has a flaw that makes it not detect t...

CURL-CVE-2017-1000257 IMAP FETCH response out of bounds read

libcurl contains a buffer overrun flaw in the IMAP handler. An IMAP FETCH response line indicates the size of the returned data, in number of bytes. When that response says the data is zero bytes, libcurl would pass on that non-existing data with a pointer and the size zero to the deliver-data...

CURL-CVE-2017-1000254 FTP PWD response parser out of bounds read

libcurl may read outside of a heap allocated buffer when doing FTP. When libcurl connects to an FTP server and successfully logs in anonymous or not, it asks the server for the current directory with the PWD command. The server then responds with a 257 response containing the path, inside double...

CURL-CVE-2017-7468 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...

CURL-CVE-2016-3739 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...

CURL-CVE-2026-80231 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...

CURL-CVE-2025-13034 No QUIC certificate pinning with GnuTLS

When using CURLOPTPINNEDPUBLICKEY option with libcurl or --pinnedpubkey with the curl tool, curl should check the public key of the server certificate to verify the peer. This check was skipped in a certain condition that would then make curl allow the connection without performing the proper...

CURL-CVE-2025-10966 missing SFTP host verification with wolfSSH

curl's code for managing SSH connections when SFTP was done using the wolfSSH powered backend was flawed and missed host verification mechanisms. This prevents curl from detecting MITM attackers and more...

CURL-CVE-2022-27782 TLS and SSH connection too eager reuse

libcurl would reuse a previously created connection even when a TLS or SSH 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, several TLS and...

CURL-CVE-2021-22926 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...

CURL-CVE-2018-0500 SMTP send heap buffer overflow

curl might overflow a heap based memory buffer when sending data over SMTP and using a reduced read buffer. When sending data over SMTP, curl allocates a separate "scratch area" on the heap to be able to escape the uploaded data properly if the uploaded data contains data that requires it. The si...

CURL-CVE-2018-1000300 FTP shutdown response buffer overflow

curl might overflow a heap based memory buffer when closing down an FTP connection with long server command replies. When doing FTP transfers, curl keeps a spare "closure handle" around internally that is used when an FTP connection gets shut down since the original curl easy handle is then alrea...

CURL-CVE-2017-2629 SSL_VERIFYSTATUS ignored

curl and libcurl support "OCSP stapling", also known as the TLS Certificate Status Request extension using the CURLOPTSSLVERIFYSTATUS option. When telling curl to use this feature, it uses that TLS extension to ask for a fresh proof of the server's certificate's validity. If the server does not...

CURL-CVE-2016-8616 case insensitive password comparison

When reusing a connection, curl was doing case insensitive comparisons of username and password with the existing connections. This means that if an unused connection with proper credentials exists for a protocol that has connection-scoped credentials, an attacker can cause that connection to be...

CURL-CVE-2014-2522 not verifying certs for TLS to IP address / Schannel

When asked to do a TLS connection HTTPS, FTPS, IMAPS, etc to a URL specified with an IP address instead of a name, libcurl would wrongly not verify the server's name in the certificate. The signature whether it was signed by a trusted CA and validity whether the date was within the certificate's...

CURL-CVE-2013-2174 URL decode buffer boundary flaw

libcurl is vulnerable to a case of bad checking of the input data which may lead to heap corruption. The function curleasyunescape decodes URL encoded strings to raw binary data. URL encoded octets are represented with %HH combinations where HH is a two-digit hexadecimal number. The decoded strin...

CURL-CVE-2005-0490 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...

CURL-CVE-2025-14017 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...

CURL-CVE-2022-32207 Non-preserved file permissions

When curl saves cookies, alt-svc and hsts data to local files, it makes the operation atomic by finalizing the operation with a rename from a temporary name to the final target filename. In that rename operation, it might accidentally widen the permissions for the target file, leaving the updated...

CURL-CVE-2022-32206 HTTP compression denial of service

curl supports "chained" HTTP compression algorithms, meaning that a server response can be compressed multiple times and potentially with different algorithms. The number of acceptable "links" in this "decompression chain" was unbounded, allowing a malicious server to insert a virtually unlimited...

CURL-CVE-2016-8622 URL unescape heap overflow via integer truncation

The URL percent-encoding decode function in libcurl is called curleasyunescape. Internally, even if this function would be made to allocate a destination buffer larger than 2GB, it would return that new length in a signed 32-bit integer variable, thus the length would get either truncated only or...