curl / Docs / Security Problems / IMAP FETCH response out of bounds read

IMAP FETCH response out of bounds read

Project curl Security Advisory, October 23rd 2017 - Permalink

VULNERABILITY

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 function.

libcurl's deliver-data function treats zero as a magic number and invokes strlen() on the data to figure out the length. The strlen() is called on a heap based buffer that might not be zero terminated so libcurl might read beyond the end of it into whatever memory lies after (or just crash) and then deliver that to the application as if it was actually downloaded.

We are not aware of any exploit of this flaw.

INFO

This bug was introduced in commit ec3bb8f727, December 2009, when the initial support for IMAP was introduced.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2017-1000257 to this issue.

CWE-126: Buffer Over-read

AFFECTED VERSIONS

curl is used by many applications, but not always advertised as such.

THE SOLUTION

In libcurl version 7.56.1, a zero bytes response is not passed on.

A patch for CVE-2017-1000257 is available.

RECOMMENDATIONS

We suggest you take one of the following actions immediately, in order of preference:

A - Upgrade curl to version 7.56.1

B - Apply the patch to your version and rebuild

C - Switch off IMAP in CURLOPT_PROTOCOLS

TIME LINE

It was reported to the curl project on October 6, 2017. We contacted distros@openwall on October 17.

curl 7.56.1 was released on October 23 2017, coordinated with the publication of this advisory.

CREDITS

Reported by Brian Carpenter, Geeknik Labs and 0xd34db347. Also independently detected by and reported by the OSS-Fuzz project. Patch by Daniel Stenberg.

Thanks a lot!