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Date: Tue, 3 Jan 2017 13:06:42 +0100
From: Peter Wu <>
Cc: Ludovic Rousseau <>
Subject: CVE Request: pcsc-lite use-after-free and double-free

Vulnerability type:
CWE-415, CWE-416


Affected Versions:
PCSC-Lite >= 1.6.0, < 1.8.20

PCSC-Lite[1] is a middleware to access a smart card using the SCard API (PC/SC).
It can be used with GnuPG, OpenSC and others for hardware like the Nitrokey and
Yubikey. These software use a client library (libpcsclite) which communicate
with a daemon (pcscd) that actually accesses the hardware.

The SCardReleaseContext function normally releases resources associated with the
given handle (including "cardsList") and clients should cease using this handle.
A malicious client can however make the daemon invoke SCardReleaseContext and
continue issuing other commands that use "cardsList", resulting in a
use-after-free.  When SCardReleaseContext is invoked multiple times, it
additionally results in a double-free of "cardsList".

The issue allows a local attacker to cause a Denial of Service, but can
potentially result in Privilege Escalation since the daemon is running as root
while any local user can connect to the Unix socket.

Fixed by patch "SCardReleaseContext: prevent use-after-free of cardsList"[2]
which is released with hpcsc-lite 1.8.20 on 30 December 2016[3].

This issue was discovered and fixed by Peter Wu (

Additional information:
The issue is confirmed for:
Arch Linux (1.8.18-1)
CentOS 7 (1.8.8-6.el7)
Debian Jessie (1.8.13-1)
using the PoC from

    $ python run/pcscd.comm
    [*] Request succeeded, possible vulnerable
    [*] Sending SCARD_RELEASE_CONTEXT (2)
    [+] Daemon crashed, it is vulnerable!

    $ sbin/pcscd --foreground --debug
    00000167 winscard_svc.c:337:ContextThread() Authorized PC/SC client
    00000011 winscard_svc.c:341:ContextThread() Thread is started: dwClientID=6, threadContext @0x610000007f40
    00000009 winscard_svc.c:359:ContextThread() Received command: RELEASE_CONTEXT from client 6
    00000008 winscard.c:226:SCardReleaseContext() Releasing Context: 0x0
    00000008 winscard_svc.c:470:ContextThread() RELEASE_CONTEXT rv=0x0 for client 6
    00000088 winscard_svc.c:359:ContextThread() Received command: RELEASE_CONTEXT from client 6
    00000012 winscard.c:226:SCardReleaseContext() Releasing Context: 0x0
    ==11540==ERROR: AddressSanitizer: heap-use-after-free on address 0x60300000d728 at pc 0x000000410490 bp 0x7f34ab4dd920 sp 0x7f34ab4dd910
    READ of size 8 at 0x60300000d728 thread T2
        #0 0x41048f in list_clear src/simclist.c:634
        #1 0x4108ba in list_destroy src/simclist.c:303
        #2 0x41843e in MSGRemoveContext src/winscard_svc.c:884
        #3 0x4194f3 in ContextThread src/winscard_svc.c:468


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