Bug 1885954 (CVE-2020-26572)

Summary:	CVE-2020-26572 opensc: stack-based buffer overflow in tcos_decipher
Product:	[Other] Security Response	Reporter:	Michael Kaplan <mkaplan>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	crypto-team, gmazyland, jjelen
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	opensc 0.21.0-rc1	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-05-18 20:36:38 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:	1885955, 1885956, 1887531
Bug Blocks:	1885958

Description Michael Kaplan 2020-10-07 10:56:11 UTC

The TCOS smart card software driver in OpenSC before 0.21.0-rc1 has a stack-based buffer overflow in tcos_decipher.

References:

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=22967
https://github.com/OpenSC/OpenSC/commit/9d294de90d1cc66956389856e60b6944b27b4817

Comment 1 Michael Kaplan 2020-10-07 10:56:51 UTC

Created opensc tracking bugs for this issue:

Affects: epel-6 [bug 1885955]
Affects: fedora-all [bug 1885956]

Comment 2 Todd Cullum 2020-10-08 20:00:43 UTC

Flaw summary:

In  the tcos_decipher() routine of src/libopensc/card-tcos.c, a call to `memcpy()` of size `crgram_len` could overflow past the end of the `sbuf` buffer, causing an out-of-bounds write. This could occur when `crgram_len` is greater than the size of `SC_MAX_APDU_BUFFER_SIZE`. The patch ensures that if `crgram_len` is greater than `sbuf - 1`, an error is returned instead.

Comment 5 Todd Cullum 2020-10-12 18:23:00 UTC

Mitigation:

This flaw can be mitigated in cases where you can use opensc without the TCOS driver enabled. In such cases, the vulnerable driver can be disabled by specifying them in /etc/opensc.conf card_drivers field in allowlist fashion.
One such example:

```
app default {
   card_drivers = cac, cac1, PIV-II;
}
```

This would only enable the cac, cac1, and PIV-II smart card drivers, and all others would be disabled, including the TCOS driver. With the TCOS driver disabled, this flaw is mitigated. It is important to list all drivers that you need in the card_drivers field so that they are not disabled too.

Comment 7 errata-xmlrpc 2021-05-18 13:35:13 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:1600 https://access.redhat.com/errata/RHSA-2021:1600

Comment 8 Product Security DevOps Team 2021-05-18 20:36:38 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2020-26572