[arch-security] [ASA-201710-2] curl: denial of service

[Levente Polyak]

Arch Linux Security Advisory ASA-201710-2
=========================================

Severity: Low
Date    : 2017-10-05
CVE-ID  : CVE-2017-1000254
Package : curl
Type    : denial of service
Remote  : Yes
Link    : https://security.archlinux.org/AVG-422

Summary
=======

The package curl before version 7.56.0-1 is vulnerable to denial of
service.

Resolution
==========

Upgrade to 7.56.0-1.

# pacman -Syu "curl>=7.56.0-1"

The problem has been fixed upstream in version 7.56.0.

Workaround
==========

None.

Description
===========

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 quotes. The returned path name is
then kept by libcurl for subsequent uses. Due to a flaw in the string
parser for this directory name, a directory name passed like this but
without a closing double quote would lead to libcurl not adding a
trailing NUL byte to the buffer holding the name. When libcurl would
then later access the string, it could read beyond the allocated heap
buffer and crash or wrongly access data beyond the buffer, thinking it
was part of the path. A malicious server could abuse this fact and
effectively prevent libcurl-based clients to work with it - the PWD
command is always issued on new FTP connections and the mistake has a
high chance of causing a segfault.

Impact
======

A malicious server can cause libcurl to segfault when connecting via
FTP leading to denial of service.

References
==========

https://curl.haxx.se/docs/adv_20171004.html
https://curl.haxx.se/CVE-2017-1000254.patch
https://github.com/curl/curl/commit/5ff2c5ff25750aba1a8f64fbcad8e5b891512584
https://security.archlinux.org/CVE-2017-1000254

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