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NTLMv2 type-3 header stack buffer overflow

Project curl Security Advisory, February 6th 2019 - Permalink


libcurl contains a stack based buffer overflow vulnerability.

The function creating an outgoing NTLM type-3 header (lib/vauth/ntlm.c:Curl_auth_create_ntlm_type3_message()), generates the request HTTP header contents based on previously received data. The check that exists to prevent the local buffer from getting overflowed is implemented wrongly (using unsigned math) and as such it does not prevent the overflow from happening.

This output data can grow larger than the local buffer if very large "nt response" data is extracted from a previous NTLMv2 header provided by the malicious or broken HTTP server.

Such a "large value" needs to be around 1000 bytes or more. The actual payload data copied to the target buffer comes from the NTLMv2 type-2 response header.

We are not aware of any exploit of this flaw.


This bug was introduced in commit 86724581b6c, January 2014.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2019-3822 to this issue.

CWE-121: Stack-based Buffer Overflow

Severity: 7.3(High)


Not every libcurl build has this code enabled. For example, it is not present when building with OpenSSL with MD4 disabled. See lib/curl_ntlm_core.h for details.

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


A patch for CVE-2019-3822


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

A - Upgrade curl to version 7.64.0

B - Apply the patch to your version and rebuild

C - Turn off NTLM authentication


It was reported to the curl project on December 30, 2018. We contacted distros@openwall on January 28.

curl 7.64.0 was released on February 6 2019, coordinated with the publication of this advisory.


Reported by Wenxiang Qian of Tencent Blade Team. Patch by Daniel Stenberg.

Huzaifa Sidhpurwala helped us clarify build details.

Thanks a lot!