Bug 1626549 (CVE-2018-16517)

Summary:	CVE-2018-16517 nasm: NULL Pointer Dereference in asm/labels.c
Product:	[Other] Security Response	Reporter:	Laura Pardo <lpardo>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	java-sig-commits, mizdebsk, nickc
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-06-10 10:37:40 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1626550, 1626551
Bug Blocks:	1626554

Description Laura Pardo 2018-09-07 15:29:07 UTC

A flaw was found in Netwide Assembler (NASM). A NULL Pointer Dereference in asm/labels.c which allows the attacker to cause a denial of service via a crafted file.


References:
https://bugzilla.nasm.us/show_bug.cgi?id=3392513
https://fakhrizulkifli.github.io/CVE-2018-16517.html

Comment 1 Laura Pardo 2018-09-07 15:29:29 UTC

Created nasm tracking bugs for this issue:

Affects: fedora-all [bug 1626550]

Comment 3 Scott Gayou 2018-10-17 16:19:28 UTC

Upstream Commit:
https://repo.or.cz/nasm.git/blobdiff/703e5658498222c3aa77e57fefb466d264abbe58..e996d28c70d45008085322b442b44a9224308548:/asm/nasm.c

Comment 4 Scott Gayou 2018-10-17 16:29:59 UTC

Doesn't reproduce on any RHEL version.

Looks like it boils down to this (presumably "correct" logic in our older release):

```c
                        if (!output_ins.label)
                            nasm_error(ERR_NONFATAL,
                                         "EQU not preceded by label");

                        else if (output_ins.label[0] != '.' ||
```

whereas mainline had:

```c
                if (!output_ins.label)
                    nasm_error(ERR_NONFATAL,
                               "EQU not preceded by label");

                if (output_ins.operands == 1 &&
                    (output_ins.oprs[0].type & IMMEDIATE) &&
                    output_ins.oprs[0].wrt == NO_SEG) {
```

Patch added back the else -- i.e. the if/then should bail if !output_ins.label.