curl FTP PWD response parser out of bounds read

2017.10.04
Credit: daniel
Risk: Medium
Local: No
Remote: Yes
CVE: N/A
CWE: N/A

FTP PWD response parser out of bounds read ========================================== Project curl Security Advisory, October 4th 2017 - [Permalink](https://curl.haxx.se/docs/adv_20171004.html) VULNERABILITY ------------- 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 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. The simple fact that this issue has remained undiscovered for this long could suggest that malformed PWD responses are rare in benign servers. We are not aware of any exploit of this flaw. INFO ---- This bug was introduced in commit [415d2e7cb7](https://github.com/curl/curl/commit/415d2e7cb7), March 2005. In libcurl version 7.56.0, the parser always zero terminates the string but also rejects it if not terminated properly with a final double quote. The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2017-1000254 to this issue. AFFECTED VERSIONS ----------------- - Affected versions: libcurl 7.7 to and including 7.55.1 - Not affected versions: libcurl < 7.7 and >= 7.56.0 curl is used by many applications, but not always advertised as such. THE SOLUTION ------------ A [patch for CVE-2017-1000254](https://curl.haxx.se/CVE-2017-1000254.patch) is available. RECOMMENDATIONS --------------- We suggest you take one of the following actions immediately, in order of preference: A - Upgrade curl to version 7.56.0 B - Apply the patch to your version and rebuild C - Switch off FTP in `CURLOPT_PROTOCOLS` TIME LINE --------- It was reported to the curl project on September 24, 2017. We contacted distros@openwall on September 25. curl 7.56.0 was released on October 4 2017, coordinated with the publication of this advisory. CREDITS ------- Reported by Max Dymond. Patch by Daniel Stenberg. Thanks a lot! -- / daniel.haxx.se

References:

https://curl.haxx.se/docs/adv_20171004.html


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