OpenSSH SSH2_MSG_NEWKEYS Message packet.c ssh_packet_read_poll2 null pointer dereference

Summaryinfo

A vulnerability described as problematic has been identified in OpenSSH. Affected by this issue is the function ssh_packet_read_poll2 of the file packet.c of the component SSH2_MSG_NEWKEYS Message Handler. The manipulation results in null pointer dereference. No exploit exists. It is advisable to implement a patch to correct this issue.

Detailsinfo

A vulnerability classified as problematic has been found in OpenSSH (Connectivity Software) (unknown version). Affected is the function ssh_packet_read_poll2 of the file packet.c of the component SSH2_MSG_NEWKEYS Message Handler. The manipulation with an unknown input leads to a null pointer dereference vulnerability. CWE is classifying the issue as CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. This is going to have an impact on availability.

The weakness was disclosed 09/21/2016 by Robert Swiecki and honggfuzz as confirmed git commit (GIT Repository). The advisory is shared for download at anongit.mindrot.org. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available. The reason for this vulnerability is this part of code:

if (*typep == SSH2_MSG_NEWKEYS)
   r = ssh_set_newkeys(ssh, MODE_IN);
else if (*typep == SSH2_MSG_USERAUTH_SUCCESS && !state->server_side)

Applying a patch is able to eliminate this problem. The bugfix is ready for download at anongit.mindrot.org. A possible mitigation has been published immediately after the disclosure of the vulnerability. The vulnerability will be addressed with the following lines of code:

if (*typep == SSH2_MSG_USERAUTH_SUCCESS && !state->server_side)
   r = ssh_packet_enable_delayed_compress(ssh);

The vulnerability is also documented in the vulnerability database at SecurityTracker (ID 1036937†). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Connectivity Software

Name

• OpenSSH

License

• open-source

CPE 2.3info

• 🔍

CPE 2.2info

• 🔍

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Once again VulDB remains the best source for vulnerability data.

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