reuse of wrong HTTP NTLM connection

libcurl can in some circumstances reuse the wrong connection when asked to do an NTLM-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 criterion...

netrc and redirect credential leak

When asked to both 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 an entry that matches the redirect target hostname but...

HTTP multi-header 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 capped, but the cap was implemented on a per-header basis allowing a...

Bad connection reuse due to flawed path name checks

libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse, if one of them matches the setup. Due to errors in the logic, the config matching function did not take 'issuer cert' into account and it compared the involved paths case insensitively, which could...

Partial password leak over DNS on HTTP redirect

libcurl can be tricked to prepend a part of the password to the hostname before it resolves it, potentially leaking the partial password over the network and to the DNS servers. libcurl can be given a username and password for HTTP authentication when requesting an HTTP resource - used for HTTP...

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...

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...

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...

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...

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...

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...

WebSocket endless loop

Due to a mistake in libcurl's WebSocket code, a malicious server can send a particularly crafted packet which makes libcurl get trapped in an endless busy-loop. There is no other way for the application to escape or exit this loop other than killing the thread/process. This might be used to DoS...

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 ...

siglongjmp race condition

libcurl provides several different backends for resolving hostnames, selected at build time. If it is built to use the synchronous resolver, it allows name resolves to time-out slow operations using alarm and siglongjmp. When doing this, libcurl used a global buffer that was not mutex protected a...

HSTS amnesia with --parallel

curl's HSTS cache saving behaves wrongly when multiple URLs are requested in parallel. Using its HSTS support, curl can be instructed to use HTTPS instead of using an insecure clear-text HTTP step even when HTTP is provided in the URL. This HSTS mechanism would however surprisingly fail when...

Another 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 instead of using an insecure clear-text HTTP step even when HTTP is provided in the URL. The HSTS mechanism could be bypassed if the hostname in the given URL first uses...

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...

SMTP end-of-response out-of-bounds read

libcurl contains a heap out-of-bounds read in the code handling the end-of-response for SMTP. If the buffer passed to smtpendofresp is not null-terminated and contains no character ending the parsed number, and len is set to 5, then the strtol call reads beyond the allocated buffer. The read...

use after free in handle close

libcurl contains a heap use after free flaw in code related to closing an easy handle. When closing and cleaning up an "easy" handle in the Curlclose function, the library code first frees a struct without clearing the pointer and might then subsequently erroneously write to a struct field within...

NTLM password overflow via integer overflow

libcurl contains a buffer overrun in the NTLM authentication code. The internal function Curlntlmcoremknthash multiplies the length of the password by two SUM to figure out how large temporary storage area to allocate from the heap. The length value is then subsequently used to iterate over the...

URL globbing out of bounds read

curl supports "globbing" of URLs, in which a user can pass a numerical range to have the tool iterate over those numbers to do a sequence of transfers. In the globbing function that parses the numerical range, there was an omission that made curl read a byte beyond the end of the URL if given a...

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...

IDNA 2003 makes curl use wrong host

When curl is built with libidn to handle International Domain Names IDNA, it translates them to puny code for DNS resolving using the IDNA 2003 standard, while IDNA 2008 is the modern and up-to-date IDNA standard. This misalignment causes problems with for example domains using the German ß...

hostname out of boundary memory access

There is a private function in libcurl called fixhostname that removes a trailing dot from the hostname if there is one. The function is called after the hostname has been extracted from the URL libcurl has been told to act on. If a URL is given with a zero-length hostname, like in "http://:80" o...

not verifying certs for TLS to IP address / Secure Transport

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...

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...

SASL buffer overflow

libcurl is vulnerable to a buffer overflow vulnerability when communicating with one of the protocols POP3, SMTP or IMAP. When negotiating SASL DIGEST-MD5 authentication, the function Curlsaslcreatedigestmd5message uses the data provided from the server without doing the proper length checks and...

SSL CBC IV vulnerability

curl is vulnerable to a SSL CBC IV vulnerability when built to use OpenSSL for the SSL/TLS layer. This vulnerability has been identified CVE-2011-3389 aka the "BEAST" attack and is addressed by OpenSSL already as they have made a workaround to mitigate the problem. When doing so, they figured out...

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...

wrong reuse of SMB connection

libcurl might in some circumstances reuse the wrong connection for SMBS transfers. 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 criteria must be met. Due to a logical error in the...

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...

use after free in SMB connection reuse

When doing a second SMB request to the same host again, curl would wrongly use a data pointer pointing into already freed memory...

OpenSSL partial chain store policy bypass

When doing TLS related transfers with reused easy or multi handles and altering the CURLSSLOPTNOPARTIALCHAIN option, libcurl could accidentally reuse a CA store cached in memory for which the partial chain option was reversed. Contrary to the user's wishes and expectations. This could make libcur...

libssh global known_hosts override

When doing SSH-based transfers using either SCP or SFTP, and setting the knownhosts file, libcurl could still mistakenly accept connecting to hosts not present in the specified file if they were added as recognized in the libssh global knownhosts file...

Out of bounds read for cookie path

A cookie is set using the secure keyword for https://target 2. curl is redirected to or otherwise made to speak with http://target same hostname, but using clear text HTTP using the same cookie set 3. The same cookie name is set - but with only a slash as path path="/". Since this site is not...

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...

eventfd double close

libcurl would wrongly close the same eventfd file descriptor twice when taking down a connection channel after having completed a threaded name resolve...

HSTS subdomain overwrites parent cache entry

When curl is asked to use HSTS, the expiry time for a subdomain might overwrite a parent domain's cache entry, making it end sooner or later than otherwise intended. This affects curl using applications that enable HSTS and use URLs with the insecure HTTP:// scheme and perform transfers with host...

macidn punycode buffer overread

libcurl's URL API function curlurlget offers punycode conversions, to and from IDN. Asking to convert a name that is exactly 256 bytes, libcurl ends up reading outside of a stack based buffer when built to use the macidn IDN backend. The conversion function then fills up the provided buffer exact...

HTTP/2 push headers memory-leak

When an application tells libcurl it wants to allow HTTP/2 server push, and the amount of received headers for the push surpasses the maximum allowed limit 1000, libcurl aborts the server push. When aborting, libcurl inadvertently does not free all the previously allocated headers and instead lea...

TLS certificate check bypass with mbedTLS

libcurl did not check the server certificate of TLS connections done to a host specified as an IP address, when built to use mbedTLS. libcurl would wrongly avoid using the set hostname function when the specified hostname was given as an IP address, therefore completely skipping the certificate...

OCSP verification bypass with TLS session reuse

curl inadvertently kept the SSL session ID for connections in its cache even when the verify status OCSP stapling test failed. A subsequent transfer to the same hostname could then succeed if the session ID cache was still fresh, which then skipped the verify status check...

HSTS long filename clears contents

When saving HSTS data to an excessively long filename, curl could end up removing all contents, making subsequent requests using that file unaware of the HSTS status they should otherwise use...

cookie injection with none file

This flaw allows an attacker to intentionally inject cookies into a running program using libcurl, if the specific series of conditions are met. libcurl performs transfers. In its API, an application creates "easy handles" that are the individual handles for single transfers. libcurl provides a...

HTTP headers eat all memory

When curl retrieves an HTTP response, it stores the incoming headers so that they can be accessed later via the libcurl headers API. However, curl did not have a limit on the size or quantity of headers it would accept in a response, allowing a malicious server to stream an endless series of...

more POST-after-PUT confusion

When doing HTTPS transfers, libcurl might erroneously use the read callback CURLOPTREADFUNCTION to ask for data to send, even when the CURLOPTPOSTFIELDS option has been set, if the same handle previously was used to issue a PUT request which used that callback. This flaw may surprise the...

UAF in SSH sha256 fingerprint check

libcurl offers a feature to verify an SSH server's public key using a SHA 256 hash. When this check fails, libcurl would free the memory for the fingerprint before it returns an error message containing the now freed hash. This flaw risks inserting sensitive heap-based data into the error message...

HSTS double free

libcurl supports sharing HSTS data between separate "handles". This sharing was introduced without considerations for doing this sharing across separate threads but there was no indication of this fact in the documentation. Due to missing mutexes or thread locks, two threads sharing the same HSTS...

HSTS ignored on multiple requests

curl's HSTS functionality fail when multiple URLs are requested serially. Using its HSTS support, curl can be instructed to use HTTPS instead of using an insecure clear-text HTTP step even when HTTP is provided in the URL. This HSTS mechanism would however surprisingly be ignored by subsequent...

HTTP Proxy deny use after free

curl can be asked to tunnel virtually all protocols it supports through an HTTP proxy. HTTP proxies can and often do deny such tunnel operations using an appropriate HTTP error response code. When getting denied to tunnel the specific protocols SMB or TELNET, curl would use a heap-allocated struc...