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...

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...

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...

POST following 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...

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...

Bad local IPv6 connection reuse

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 the IPv6 address zone id into account which could lead to libcurl reusing the wrong connection...

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...

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...

TLS session caching disaster

libcurl can be tricked into using already freed memory when a new TLS session is negotiated or a client certificate is requested on an existing connection. For example, this can happen when a TLS server requests a client certificate on a connection that was established without one. A malicious...

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...

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...

FTP path trickery leads to NIL byte out of bounds write

curl can be fooled into writing a zero byte out of bounds. This bug can trigger when curl is told to work on an FTP URL, with the setting to only issue a single CWD command --ftp-method singlecwd or the libcurl alternative CURLOPTFTPFILEMETHOD. curl then URL-decodes the given path, calls strlen o...

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...

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...

URL file scheme drive letter buffer overflow

When libcurl is given either 1. a file: URL that does not use two slashes following the colon, or 2. is told that file is the default scheme to use for URLs without scheme ... and the given path starts with a drive letter and libcurl is built for Windows or DOS, then libcurl would copy the path...

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...

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...

OOB write via unchecked multiplication

In libcurl's base64 encode function, the output buffer is allocated as follows without any checks on insize: malloc insize 4 / 3 + 4 On systems with 32-bit addresses in userspace e.g. x86, ARM, x32, the multiplication in the expression wraps around if insize is at least 1GB of data. If this...

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...

curl_getdate read out of bounds

The curlgetdate converts a given date string into a numerical timestamp and it supports a range of different formats and possibilities to express a date and time. The underlying date parsing function is also used internally when parsing for example HTTP cookies possibly received from remote serve...

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...

cookie injection for other servers

If cookie state is written into a cookie jar file that is later read back and used for subsequent requests, a malicious HTTP server can inject new cookies for arbitrary domains into said cookie jar. The issue pertains to the function that loads cookies into memory, which reads the specified file...

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...

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...

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...

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...

cookie parser out of boundary memory access

libcurl supports HTTP "cookies" as documented in RFC 6265. Together with each individual cookie there are several different properties, but for this vulnerability we focus on the associated "path" element. It tells information about for which path on a given host the cookie is valid. The internal...

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...

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...

cookie domain tailmatch

libcurl is vulnerable to a cookie leak vulnerability when doing requests across domains with matching tails. When communicating over HTTPS and having libcurl's cookie engine enabled, libcurl stores and holds cookies for use when subsequent requests are done to hosts and paths that match those kep...

URL sanitization vulnerability

curl is vulnerable to a data injection attack for certain protocols through control characters embedded or percent-encoded in URLs. When parsing URLs, libcurl's parser is liberal and only parses as little as possible and lets as much as possible through as long as it can figure out what to do. In...

inappropriate GSSAPI delegation

When doing GSSAPI authentication, libcurl unconditionally performs credential delegation. This hands the server a copy of the client's security credentials, allowing the server to impersonate the client to any other using the same GSSAPI mechanism. This is obviously a sensitive operation, which...

data callback excessive length

When downloading data, libcurl hands it over to the application using a callback that is registered by the client software. libcurl then calls that function repeatedly with data until the transfer is complete. The callback is documented to receive a maximum data size of 16K CURLMAXWRITESIZE. Usin...

Arbitrary File Access

When told to follow a "redirect" automatically, libcurl does not question the new target URL but follows it to any new URL that it understands. As libcurl supports FILE:// URLs, a rogue server can thus "trick" a libcurl-using application to read a local file instead of the remote one. This is a...

TFTP Packet Buffer Overflow

libcurl uses the given file part of a TFTP URL in a manner that allows a malicious user to overflow a heap-based memory buffer due to the lack of boundary check. This overflow happens if you pass in a URL with a TFTP protocol prefix "tftp://", using a valid host and a path part that is longer tha...

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...

printf floating point buffer overflow

libcurl's implementation of the printf functions triggers a buffer overflow when doing a large floating point output. The bug occurs when the conversion outputs more than 255 bytes. The flaw happens because the floating point conversion is using system functions without the correct boundary check...

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...