(Actually the function Curl_ossl_close() is on line 855 in ssluse.c of the version 7.24 and i guess at line 865 in latest)

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** [bugs:#1236] Curl double-free with pkcs12 handling**
**Status:** open
**Created:** Fri May 31, 2013 10:06 PM UTC by Nikaiw
**Last Updated:** Mon Jun 10, 2013 08:49 AM UTC
**Owner:** nobody
Summary :
-------
There is a double free bug in curl when using p12 client certificate to connect to an https server.
Steps to reproduce :
------------------
Connect to any https server using a client certificate in pkcs12 format.
curl -vvv --cert yourcertificate.p12:yourpassword --cert-type P12 https://yourserver.com
eg:
* About to connect() to ************ port 443 (#0)
*   Trying **********...
* Connected to ********** (*.*.*.*) port 443 (#0)
* successfully set certificate verify locations:
*   CAfile: none
  CApath: /etc/ssl/certs
* SSLv3, TLS handshake, Client hello (1):
* SSLv3, TLS handshake, Server hello (2):
* SSLv3, TLS handshake, CERT (11):
* SSLv3, TLS alert, Server hello (2):
* SSL certificate problem: unable to get local issuer certificate
* Closing connection 0
Erreur de segmentation (core dumped)
Bug is 100% reproducible.
Affected version :
----------------
Affected version are curl-7.24 to 7.30. 
Details :
--------
Bug was introduced in following commit to fix a memory leak: 
https://github.com/bagder/curl/commit/6ea7acf5a96786f7514be4fbce174cdc8bedfdd1
on line 512 of ssluse.c:  sk_X509_pop_free(ca, X509_free);
curl is freeing data related to the handling of the certificate which may have already being freed by SSL_CTX_free call made on line 865 of ssluse.c when we are closing the ssl connexion.
Here is a valgrind stacktrace:
==4136== Invalid free() / delete / delete[] / realloc()
==4136==    at 0x4C2BA6C: free (vg_replace_malloc.c:446)
==4136==    by 0x5B964EC: CRYPTO_free (mem.c:397)
==4136==    by 0x5C4029F: asn1_item_combine_free (tasn_fre.c:176)
==4136==    by 0x5C40484: ASN1_item_free (tasn_fre.c:71)
==4136==    by 0x5C1E96F: sk_pop_free (stack.c:283)
==4136==    by 0x590F806: SSL_CTX_free (ssl_lib.c:1947)
==4136==    by 0x4E67BD4: Curl_ossl_close (ssluse.c:865)
==4136==    by 0x4E89822: Curl_ssl_close (sslgen.c:421)
==4136==    by 0x4E60906: Curl_disconnect (url.c:2565)
==4136==    by 0x4E81B40: multi_runsingle (multi.c:1637)
==4136==    by 0x4E81D54: curl_multi_perform (multi.c:1708)
==4136==    by 0x4E76CDC: curl_easy_perform (easy.c:448)
==4136==  Address 0x6636d00 is 0 bytes inside a block of size 184 free'd
==4136==    at 0x4C2BA6C: free (vg_replace_malloc.c:446)
==4136==    by 0x5B964EC: CRYPTO_free (mem.c:397)
==4136==    by 0x5C4029F: asn1_item_combine_free (tasn_fre.c:176)
==4136==    by 0x5C40484: ASN1_item_free (tasn_fre.c:71)
==4136==    by 0x5C1E96F: sk_pop_free (stack.c:283)
==4136==    by 0x4E67378: cert_stuff (ssluse.c:510)
==4136==    by 0x4E68F54: ossl_connect_step1 (ssluse.c:1524)
==4136==    by 0x4E6BBC8: ossl_connect_common (ssluse.c:2433)
==4136==    by 0x4E6BE46: Curl_ossl_connect_nonblocking (ssluse.c:2522)
==4136==    by 0x4E890A2: Curl_ssl_connect_nonblocking (sslgen.c:218)
==4136==    by 0x4E49D5C: https_connecting (http.c:1345)
==4136==    by 0x4E49CBA: Curl_http_connect (http.c:1315)
I'm not sure the bug is exploitable nor i see any practical case.
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