ASA-2019-00483 – Das U-Boot: Unbounded memcpy with a failed length check at nfs_lookup_reply()

Posted on by Allele Security Intelligence in Alerts

Allele Security Alert

ASA-2019-00483

Identifier(s)

ASA-2019-00483, CVE-2019-14196

Title

Unbounded memcpy with a failed length check at nfs_lookup_reply()

Vendor(s)

DENX Software Engineering

Product(s)

Das U-Boot

Affected version(s)

Unknown

Fixed version(s)

Unknown

Proof of concept

Unknown

Description

This problem exists in the nfs_lookup_reply() function that again parses an nfs reply coming from the network. It parses 4 bytes and uses them as length for a memcpy in two different locations.

Technical details

A length check happens to make sure it is not bigger than the allocated buffer. Unfortunately, this check can be bypassed with a negative value that would lead later to a large buffer overflow.

filefh3_length = ntohl(rpc_pkt.u.reply.data\[1]);
if (filefh3_length > NFS3_FHSIZE)
    filefh3_length  = NFS3_FHSIZE;

memcpy(filefh, rpc_pkt.u.reply.data + 2, filefh3_length);
The destination buffer filefh is a global one that can hold up to 64 bytes.

Credits

Fermín Serna, Pavel Avgustinov and Kevin Backhouse

Reference(s)

U-Boot RCE Vulnerabilities Affecting IoT Devices
https://blog.semmle.com/uboot-remote-code-execution-vulnerability/

U-Boot NFS RCE Vulnerabilities (CVE-2019-14192)
https://blog.semmle.com/uboot-rce-nfs-vulnerability/

[U-Boot] Remote code execution vulnerabilities in U-Boot’s NFS and other IP parsing code
https://lists.denx.de/pipermail/u-boot/2019-July/378001.html

CVE-2019-14196
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-14196

CVE-2019-14196
https://nvd.nist.gov/vuln/detail/CVE-2019-14196

If there is any error in this alert or you wish a comprehensive analysis, let us know.

Last modified: August 8, 2019

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