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SASL password overflow via integer overflow

Project curl Security Advisory, October 31st 2018 - Permalink


libcurl contains a buffer overrun in the SASL authentication code.

The internal function Curl_auth_create_plain_message fails to correctly verify that the passed in lengths for name and password are not too long, then calculates a buffer size to allocate.

On systems with a 32 bit size_t, the math to calculate the buffer size triggers an integer overflow when the username length exceeds 1GB and the password name length is close to 2GB in size. This integer overflow usually causes a very small buffer to actually get allocated instead of the intended very huge one, making the use of that buffer end up in a heap buffer overflow.

(This bug is very similar to CVE-2018-14618.)


The affected function can only be invoked when using POP3(S), IMAP(S) or SMTP(S).

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2018-16839 to this issue.

CWE-131: Incorrect Calculation of Buffer Size

Severity: Low


This issue is only present on 32 bit systems. It also requires the username field to use more than 2GB of memory, which should be rare.

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


In libcurl version 7.62.0, the integer overflow is avoided. An error is returned if a too long username is attempted.


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

A - Upgrade curl to version 7.62.0

B - Apply the patch to your version and rebuild

C - Put length restrictions on the username field you can pass to libcurl


It was reported to the curl project on September 6, 2018. We contacted distros@openwall on October 22.

curl 7.62.0 was released on October 31 2018, coordinated with the publication of this advisory.


Thanks a lot!