HTTP/2 C library and tools

Nghttp2 v1.31.1

We have released nghttp2 v1.31.1.

This release addresses following security issue.

Security Advisory

CVE-2018-1000168: Denial of service due to NULL pointer dereference.


If ALTSVC frame is received by libnghttp2 and it is larger than it can accept, the pointer field which points to ALTSVC frame payload is left NULL. Later libnghttp2 attempts to access another field through the pointer, and gets segmentation fault.

ALTSVC frame is defined by RFC 7838.

The largest frame size libnghttp2 accept is by default 16384 bytes.

Receiving ALTSVC frame is disabled by default. Application has to enable it explicitly by calling nghttp2_option_set_builtin_recv_extension_type(opt, NGHTTP2_ALTSVC).

Transmission of ALTSVC is always enabled, and it does not cause this vulnerability.

ALTSVC frame is expected to be sent by server, and received by client as defined in RFC 7838.

Client and server are both affected by this vulnerability if the reception of ALTSVC frame is enabled. As written earlier, it is useless to enable reception of ALTSVC frame on server side. So, server is generally safe unless application accidentally enabled the reception of ALTSVC frame.

Affected Versions

  • Affected versions: nghttp2 >= 1.10.0 and nghttp2 <= v1.31.0
  • Not affected versions: nghttp2 >= 1.31.1

The Solution

Upgrade to nghttp2 v1.31.1.

If the upgrade cannot be possible:

For client, disable ALTSVC, removing the call to nghttp2_option_set_builtin_recv_extension_type(opt, NGHTTP2_ALTSVC)

For server, because it is never expected to receive ALTSVC, just remove nghttp2_option_set_builtin_recv_extension_type(opt, NGHTTP2_ALTSVC).

Time Line

It was first reported to the nghttp2 team April 4 2018.

nghttp2 v1.31.1 was released on April 12 2018.


Reported by Jordan Zebor at F5 Networks, and James M Snell from Node.js project. Fixed by the nghttp2 team.

Thank you for all who involved.

This security advisory format is inspired from curl/libcurl project.