Bug 1671377 (CVE-2018-19827)

Summary:	CVE-2018-19827 libsass: Use-after-free in SharedPtr class resulting in a denial of service
Product:	[Other] Security Response	Reporter:	Andrej Nemec <anemec>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	aurelien, fmuellner, rschiron
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	A type confusion flaw was discovered in libsass in Expand::operator() in expand.cpp. An attacker could use this flaw to make an application that uses libsass crash or execute arbitrary code.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-06-10 10:47:00 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:	1671395, 1671396, 1677702
Bug Blocks:	1671393

Description Andrej Nemec 2019-01-31 14:01:50 UTC

In LibSass 3.5.5, a use-after-free vulnerability exists in the SharedPtr class in SharedPtr.cpp (or SharedPtr.hpp) that may cause a denial of service (application crash) or possibly have unspecified other impact.

Upstream issue:

https://github.com/sass/libsass/issues/2782

Comment 1 Andrej Nemec 2019-01-31 14:16:30 UTC

Created libsass tracking bugs for this issue:

Affects: epel-7 [bug 1671396]
Affects: fedora-all [bug 1671395]

Comment 2 Riccardo Schirone 2019-02-15 14:49:10 UTC

Upstraem patch:
https://github.com/sass/libsass/commit/67a3f4ff9b790ed016197e6da4ef4e1d4c9da09f

Comment 3 Riccardo Schirone 2019-02-15 15:24:08 UTC

The use-after-free reported by ASAN is actually caused by a type confusion. In particular, function Expand::operator() in expand.cpp calls Expand::selector() which returns a Selector_List_Obj object. However, the result is assigned to a variable of type Selector_List_Ptr. This can lead to accessing invalid memory or possibly executing arbitrary code.