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...

gzip integer overflow

When libcurl is asked to perform automatic gzip decompression of content-encoded HTTP responses with the CURLOPTACCEPTENCODING option, using zlib 1.2.0.3 or older, an attacker-controlled integer overflow would make libcurl perform a buffer overflow...

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...

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...

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...

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...

ASN.1 date parser overread

libcurl's ASN1 parser code has the GTime2str function, used for parsing an ASN.1 Generalized Time field. If given an syntactically incorrect field, the parser might end up using -1 for the length of the time fraction, leading to a strlen getting performed on a pointer to a heap buffer area that i...

freeing stack buffer in utf8asn1str

libcurl's ASN1 parser has this utf8asn1str function used for parsing an ASN.1 UTF-8 string. It can detect an invalid field and return error. Unfortunately, when doing so it also invokes free on a 4 byte local stack buffer. Most modern malloc implementations detect this error and immediately abort...

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...

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...

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...

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...

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 ...

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...

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...

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...

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...

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...

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 ...

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...

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...

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...

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...

HTTP proxy double free

If curl is told to use an HTTP proxy for a transfer with a non-HTTPS URL, it sets up the connection to the remote server by issuing a CONNECT request to the proxy, and then tunnels the rest of protocol through. An HTTP proxy might refuse this request HTTP proxies often only allow outgoing...

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...

.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...

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 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...

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...

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...

percent-encoded path separator in URL host

The curl URL parser wrongly accepts percent-encoded URL separators like '/' when decoding the hostname part of a URL, making it a different URL using the wrong hostname when it is later retrieved. For example, a URL like http://example.com%2F10.0.0.1/, would be allowed by the parser and get...

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...

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...

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...

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...

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...

TELNET stack contents disclosure again

curl supports the -t command line option, known as CURLOPTTELNETOPTIONS in libcurl. This rarely used option is used to send variable=content pairs to TELNET servers. Due to flaw in the option parser for sending NEWENV variables, libcurl could be made to pass on uninitialized data from a stack bas...

Wrong content via Metalink not discarded

When curl is instructed to download content using the Metalink feature, the contents is verified against a hash provided in the Metalink XML file. The Metalink XML file points out to the client how to get the same content from a set of different URLs, potentially hosted by different servers and t...

TELNET stack contents disclosure

curl supports the -t command line option, known as CURLOPTTELNETOPTIONS in libcurl. This rarely used option is used to send variable=content pairs to TELNET servers. Due to flaw in the option parser for sending NEWENV variables, libcurl could be made to pass on uninitialized data from a stack bas...

TLS 1.3 session ticket proxy host mix-up

Enabled by default, libcurl supports the use of TLS 1.3 session tickets to resume previous TLS sessions to speed up subsequent TLS handshakes. When using an HTTPS proxy and TLS 1.3, libcurl can confuse session tickets arriving from the HTTPS proxy but work as if they arrived from the remote serve...

FTP wildcard stack overflow

libcurl offers a wildcard matching functionality, which allows a callback set with CURLOPTCHUNKBGNFUNCTION to return information back to libcurl on how to handle a specific entry in a directory when libcurl iterates over a list of all available entries. When this callback returns...

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...

trusting FTP PASV responses

When curl performs a passive FTP transfer, it first tries the EPSV command and if that is not supported, it falls back to using PASV. Passive mode is what curl uses by default. A server response to a PASV command includes the IPv4 address and port number for the client to connect back to in order...

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...

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...

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...

TFTP small blocksize heap buffer overflow

libcurl contains a heap buffer overflow in the function tftpreceivepacket that receives data from a TFTP server. It can call recvfrom with the default size for the buffer rather than with the size that was used to allocate it. Thus, the content that might overwrite the heap memory is controlled b...