Bug 1626549 – CVE-2018-16517 nasm: NULL Pointer Dereference in asm/labels.c

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Bug 1626549 - (CVE-2018-16517) CVE-2018-16517 nasm: NULL Pointer Dereference in asm/labels.c

Summary:	CVE-2018-16517 nasm: NULL Pointer Dereference in asm/labels.c

Status:	NEW

Aliases:	CVE-2018-16517

Product:	Security Response
Classification:	Other
Component:	vulnerability (Show other bugs)
Sub Component:
Version:	unspecified
Hardware:	All Linux

Priority	low Severity low
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Assigned To:	Red Hat Product Security
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URL:
Whiteboard:	impact=low,public=20180905,reported=2...
Keywords:	Security

Depends On:	1626550 1626551
Blocks:	1626554
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Reported:	2018-09-07 11:29 EDT by Laura Pardo
Modified:	2018-10-17 12:29 EDT (History)
CC List:	3 users (show)

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Description Laura Pardo 2018-09-07 11:29:07 EDT

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 11:29:29 EDT

Created nasm tracking bugs for this issue:

Affects: fedora-all [bug 1626550]

Comment 3 Scott Gayou 2018-10-17 12:19:28 EDT

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

Comment 4 Scott Gayou 2018-10-17 12:29:59 EDT

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.

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