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TFTP receive buffer overflow

Project curl Security Advisory, May 22nd 2019 - Permalink


libcurl contains a heap buffer overflow in the function (tftp_receive_packet()) that recevives data from a TFTP server. It calls recvfrom() with the default size for the buffer rather than with the size that was used to allocate it. Thus, the content that might overwrite the heap memory is entirely controlled by the server.

The flaw exists if the user selects to use a "blksize" of 504 or smaller (default is 512). The smaller size that is used, the larger the possible overflow becomes.

Users chosing a smaller size than default should be rare as the primary use case for changing the size is to make it larger.

It is rare for users to use TFTP across the Internet. It is most commonly used within local networks.

We are not aware of any exploit of this flaw.


This bug was introduced in January 2009 in commit 0516ce7786e95.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2019-5436 to this issue.

CWE-122: Heap-based Buffer Overflow

Severity: Low


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


A fix for CVE-2019-5436


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

A - Upgrade curl to version 7.65.0

B - Apply the patch to your version and rebuild

C - do not use TFTP with curl


The issue was reported to the curl project on April 29, 2019. The patch was communicated to the reporter on April 29, 2019. We contacted distros@openwall on May 15.

curl 7.65.0 was released on May 22 2019, coordinated with the publication of this advisory.


Thanks a lot!