A vulnerability, which was classified as problematic, has been found in NASM (Programming Tool Software) (the affected version is unknown). Affected by this issue is an unknown code of the file asm/labels.c. The manipulation with an unknown input leads to a null pointer dereference vulnerability. Using CWE to declare the problem leads to 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. Impacted is availability. CVE summarizes:

asm/labels.c in Netwide Assembler (NASM) is prone to NULL Pointer Dereference, which allows the attacker to cause a denial of service via a crafted file.

The bug was discovered 09/05/2018. The weakness was published 09/06/2018 as Bug 3392513 as not defined bug report (Bugzilla). The advisory is shared for download at bugzilla.nasm.us. This vulnerability is handled as CVE-2018-16517 since 09/05/2018. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. Technical details as well as a public exploit are known.

A public exploit has been developed by Fakhri Zulkifli in ANSI C and been published 9 months after the advisory. The exploit is available at exploit-db.com. It is declared as proof-of-concept. The vulnerability was handled as a non-public zero-day exploit for at least 1 days. During that time the estimated underground price was around $0-$5k. The code used by the exploit is:

if (i == TOKEN_ID || (insn_is_label && i == TOKEN_INSN)) {    <-- not taken
	/* there's a label here */
	first = false;
	result->label = tokval.t_charptr;
	i = stdscan(NULL, &tokval);
	if (i == ':') {         /* skip over the optional colon */
		i = stdscan(NULL, &tokval);
	} else if (i == 0) {
		nasm_error(ERR_WARNING | ERR_WARN_OL | ERR_PASS1,
			  "label alone on a line without a colon might be in error");
	}
	if (i != TOKEN_INSN || tokval.t_integer != I_EQU) {
		/*
		 * FIXME: location.segment could be NO_SEG, in which case
		 * it is possible we should be passing 'absolute.segment'. Look into this.
		 * Work out whether that is *really* what we should be doing.
		 * Generally fix things. I think this is right as it is, but
		 * am still not certain.
		 */
		define_label(result->label,
					 in_absolute ? absolute.segment : location.segment,
					 location.offset, true);

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at Exploit-DB (46726).

Productinfo

Type

• Programming Tool Software

Name

• NASM

License

• open-source

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CPE 2.2info

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