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...

SFTP path ~ resolving discrepancy

curl supports SFTP transfers. curl's SFTP implementation offers a special feature in the path component of URLs: a tilde character as the first path element in the path to denotes a path relative to the user's home directory. This is supported because of wording in the once proposed to-become RFC...

TELNET option IAC injection

curl supports communicating using the TELNET protocol and as a part of this it offers users to pass on username and "telnet options" for the server negotiation. Due to lack of proper input scrubbing and without it being the documented functionality, curl would pass on username and telnet options ...

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...

.netrc parser out-of-bounds access

curl can be told to parse a .netrc file for credentials. If that file ends in a line with consecutive non-white space letters and no newline, curl could read past the end of the stack-based buffer, and if the read works, write a zero byte possibly beyond its boundary. This does in most cases caus...

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...

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 removes wrong file on error

curl might remove the wrong file when --no-clobber is used together with --remove-on-error. The --remove-on-error option tells curl to remove the output file when it returns an error, and not leave a partial file behind. The --no-clobber option prevents curl from overwriting a file if it already...

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...

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,...

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...

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...

NTLM type-2 out-of-bounds buffer read

libcurl contains a heap buffer out-of-bounds read flaw. The function handling incoming NTLM type-2 messages lib/vauth/ntlm.c:ntlmdecodetype2target does not validate incoming data correctly and is subject to an integer overflow vulnerability. Using that overflow, a malicious or broken NTLM server...

warning message out-of-buffer read

curl contains a heap out of buffer read vulnerability. The command line tool has a generic function for displaying warning and informational messages to stderr for various situations. For example if an unknown command line argument is used, or passed to it in a "config" file. This display functio...

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...

NTLM buffer overflow via integer overflow

libcurl contains a buffer overrun flaw in the NTLM authentication code. The internal function Curlntlmcoremkntlmv2hash sums up the lengths of the username + password = SUM and multiplies the sum by two = SIZE to figure out how large storage to allocate from the heap. The SUM value is subsequently...

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...

FILE buffer read out of bounds

When asking to get a file from a file:// URL, libcurl provides a feature that outputs meta-data about the file using HTTP-like headers. The code doing this would send the wrong buffer to the user stdout or the application's provide callback, which could lead to other private data from the heap to...

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...

uninitialized random

libcurl's new internal function that returns a good 32-bit random value was implemented poorly and overwrote the pointer instead of writing the value into the buffer the pointer pointed to. This random value is used to generate nonces for Digest and NTLM authentication, for generating boundary...

invalid URL parsing with '#'

curl does not parse the authority component of the URL correctly when the host name part ends with a hash character, and could instead be tricked into connecting to a different host. This may have security implications if you for example use a URL parser that follows the RFC to check for allowed...

Use after free via shared cookies

libcurl explicitly allows users to share cookies between multiple easy handles that are concurrently employed by different threads. When cookies to be sent to a server are collected, the matching function collects all cookies to send and the cookie lock is released immediately afterwards. That...

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...

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...

remote filename path traversal in curl tool for Windows

curl does not sanitize colons in a remote filename that is used as the local filename. This may lead to a vulnerability on systems where the colon is a special path character. Currently Windows is the only OS where this vulnerability applies. curl offers command line options --remote-name also...

NTLM credentials not-checked for proxy connection reuse

libcurl reuses NTLM-authenticated proxy connections without properly making sure that the connection was authenticated with the same credentials as set for this transfer. libcurl maintains a pool of connections after a transfer has completed. The pool of connections is then gone through when a ne...

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...

Reusing authenticated connection when unauthenticated

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 NTLM authenticated, the entire connection becomes authenticated and not only the specific HTTP request which is...

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...

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...

cert name check ignore OpenSSL

libcurl is vulnerable to a case of missing out the checking of the certificate CN or SAN name field when the digital signature verification is turned off. libcurl offers two separate and independent options for verifying a server's TLS certificate. CURLOPTSSLVERIFYPEER and CURLOPTSSLVERIFYHOST. T...

embedded zero in cert name

SSL and TLS Server certificates contain one or more fields with server name or otherwise matching patterns. These strings are stored as content and length within the certificate, and thus there is no particular terminating character. curl's OpenSSL interfacing code did faulty assumptions about...

GnuTLS insufficient cert verification

libcurl when built to use GnuTLS fails to verify that a peer's certificate has not already expired or has not yet become valid. This allows malicious servers to present certificates to libcurl that were not rejected properly. Notably, the CA certificate and common name checks are still in place...

NTLM Buffer Overflow

libcurl's NTLM function can overflow a stack-based buffer if given a too long username or domain name. This would happen if you enable NTLM authentication and either: A - pass in a username and domain name to libcurl that together are longer than 192 bytes B - allow libcurl to follow HTTP...

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...

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...

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...

QUIC certificate check bypass with wolfSSL

libcurl skips the certificate verification for a QUIC connection under certain conditions, when built to use wolfSSL. If told to use an unknown/bad cipher or curve, the error path accidentally skips the verification and returns OK, thus ignoring any certificate problems...

Usage of disabled protocol

When a protocol selection parameter option disables all protocols without adding any then the default set of protocols would remain in the allowed set due to an error in the logic for removing protocols. The below command would perform a request to curl.se with a plaintext protocol which has been...

cookie mixed case PSL bypass

This flaw allows a malicious HTTP server to set "super cookies" in curl that are then passed back to more origins than what is otherwise allowed or possible. This allows a site to set cookies that then would get sent to different and unrelated sites and domains. It could do this by exploiting a...

GSS delegation too eager connection reuse

libcurl would reuse a previously created connection even when the GSS delegation CURLOPTGSSAPIDELEGATION option had been changed that could have changed the user's permissions in a second transfer. libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if...

FTP too eager connection reuse

libcurl would reuse a previously created FTP connection even when one or more options had been changed that could have made the effective user a different one, thus leading to doing the second transfer with the wrong credentials. libcurl keeps previously used connections in a connection pool for...

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...

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...

Set-Cookie denial of service

A malicious server can serve excessive amounts of Set-Cookie: headers in a HTTP response to curl and curl stores all of them. A sufficiently large amount of big cookies make subsequent HTTP requests to this, or other servers to which the cookies match, create requests that become larger than the...

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 ...

CERTINFO never-ending busy-loop

libcurl provides the CURLOPTCERTINFO option to allow applications to request details to be returned about a TLS server's certificate chain. Due to an erroneous function, a malicious server could make libcurl built with NSS get stuck in a never-ending busy-loop when trying to retrieve that...

Auth/cookie leak on redirect

curl might leak authentication or cookie header data on HTTP redirects to the same host but another port number. When asked to send custom headers or cookies in its HTTP requests, curl sends that set of headers only to the host which name is used in the initial URL, so that redirects to other hos...