Attachment 712481 Details for Bug 804920 – Local copy of the Mu Dynamics advisory text

Local copy of the Mu Dynamics advisory text

mu-dynamics-gnutls-advisories-201202.txt.asc (text/plain), 15.53 KB, created by Tomas Hoger on 2013-03-19 09:30:23 UTC

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>Mu Dynamics, Inc. Security Advisories MU-201202-01 and MU-201202-02 for GnuTLS and Libtasn1
>
>TLS record handling vulnerability in GnuTLS [MU-201202-01]
>ASN.1 length decoding vulnerability in Libtasn1 [MU-201202-02]
>
>20 March 2012
>
>http://blog.mudynamics.com/2012/03/20/gnutls-and-libtasn1-vulns/
>http://labs.mudynamics.com/advisories.html
>
>Affected Products/Versions:
>
>* libgnutls up to 3.0.16.
>* libtasn1 up to 2.11.
>
>Product Overview:
>
>GnuTLS is an open source implementation of SSL, TLS and DTLS, with APIs for 
>encrypted network communications, along with X.509, PKCS #12, OpenPGP, and 
>other security data types.
>
>Analysis:
>
>Details for TLS record handling vulnerability in GnuTLS [MU-201202-01]:
>
>The block cipher decryption logic in GnuTLS assumed that a record containing 
>any data which was a multiple of the block size was valid for further 
>decryption processing, leading to a heap corruption vulnerability.
>
>The bug can be reproduced in GnuTLS 3.0.14 by creating a corrupt 
>GenericBlockCipher struct with a valid IV, while everything else is stripped 
>off the end, while the handshake message length retains its original value:
>
>struct {
>    opaque IV[SecurityParameters.record_iv_length];
>    // corrupt: below items not sent
>    /*
>    block-ciphered struct {
>        opaque content[TLSCompressed.length];
>        opaque MAC[SecurityParameters.mac_length];
>        uint8 padding[GenericBlockCipher.padding_length];
>        uint8 padding_length;
>    };
>    */
>} GenericBlockCipher;
>
>This will cause a segmentation fault, when the ciphertext_to_compressed 
>function tries to give decrypted data to _gnutls_auth_cipher_add_auth for HMAC 
>verification, even though the data length is invalid, and it should have 
>returned GNUTLS_E_DECRYPTION_FAILED or GNUTLS_E_UNEXPECTED_PACKET_LENGTH 
>instead, before _gnutls_auth_cipher_add_auth was called.
>
>Since the error was not returned soon enough, all of the various operations 
>ciphertext_to_compressed performs: i.e. setting the IV, removing the padding, 
>setting the "true" data length with the padding stripped, checking the padding 
>size and padding payload and verifying HMAC could all reference undefined, 
>unallocated, or uninitialized memory.
>
>There could be similar ways to reproduce this for AEAD ciphers due to the 
>various flows through this code, but we did not attempt to do this, and see it 
>as a topic for further investigation.
>
>Below we trace the execution of the ciphertext_to_compressed function from 
>lib/gnutls_cipher.c. The unsafe operations and missed opportunities to return 
>before the heap corruption happens are marked with "***** ... *****" :
>
> 433    static int
> 434    ciphertext_to_compressed (gnutls_session_t session,
> 435                              gnutls_datum_t *ciphertext, 
> 436                              uint8_t * compress_data,
> 437                              int compress_size,
> 438                              uint8_t type, record_parameters_st * params, 
> 439                              uint64* sequence)
> 440    {
>...
> 511        case CIPHER_BLOCK:
> 512          if (ciphertext->size < MAX(blocksize, tag_size) || (ciphertext->size % blocksize != 0)) ***** UNSAFE *****
> 513            return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
> 514    
> 515          /* ignore the IV in TLS 1.1+
> 516           */
> 517          if (explicit_iv)
> 518            {
> 519              _gnutls_auth_cipher_setiv(&params->read.cipher_state,
> 520                ciphertext->data, blocksize);
> 521    
> 522              ciphertext->size -= blocksize;
> 523              ciphertext->data += blocksize;
> 524    
> 525              if (ciphertext->size == 0) ***** UNSAFE *****
> 526                {
> 527                  gnutls_assert ();
> 528                  return GNUTLS_E_DECRYPTION_FAILED;
> 529                }
> 530            }
>...
> 537          if ((ret =
> 538               _gnutls_cipher_decrypt (&params->read.cipher_state.cipher,
> 539                 ciphertext->data, ciphertext->size)) < 0)
> 540            return gnutls_assert_val(ret);
> 541    
> 542          pad = ciphertext->data[ciphertext->size - 1] + 1;   /* pad */
> 543    
> 544          if ((int) pad > (int) ciphertext->size - tag_size)
> 545            {
> 546              gnutls_assert ();
> 547              _gnutls_record_log
> 548                ("REC[%p]: Short record length %d > %d - %d (under attack?)\n",
> 549                 session, pad, ciphertext->size, tag_size); ***** Message Appears During The Attack *****
> 550              /* We do not fail here. We check below for the
> 551               * the pad_failed. If zero means success.
> 552               */
> 553              pad_failed = GNUTLS_E_DECRYPTION_FAILED; ***** Execution Continues Anyway *****
> 554              pad %= blocksize;
> 555            }
> 556    
> 557          length = ciphertext->size - tag_size - pad;
> 558    
> 559          /* Check the padding bytes (TLS 1.x) */
>...
> 577          /* Pass the type, version, length and compressed through
> 578           * MAC.
> 579           */
> 580          preamble_size =
> 581            make_preamble (UINT64DATA(*sequence), type,
> 582                           length, ver, preamble);
> 583          ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, preamble, preamble_size);
> 584          if (ret < 0)
> 585            return gnutls_assert_val(ret);
> 586    
> 587          ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, ciphertext->data, length); ***** UNSAFE, crashes here *****
> 588          if (ret < 0)
> 589            return gnutls_assert_val(ret); ***** Crashes Before Error Is Returned *****
>... 
>
>The segmentation fault appears as follows in GDB:
>
>Program received signal SIGSEGV, Segmentation fault.
>0x003b9946 in _nettle_sha256_compress (state=0x807f128, 
>    input=0x808f000 <Address 0x808f000 out of bounds>, k=0x3cdb60)
>    at sha256-compress.c:111
>111	sha256-compress.c: No such file or directory.
>	in sha256-compress.c
>(gdb) bt
>#0  0x003b9946 in _nettle_sha256_compress (state=0x807f128, 
>    input=0x808f000 <Address 0x808f000 out of bounds>, k=0x3cdb60)
>    at sha256-compress.c:111
>#1  0x003b961b in nettle_sha256_update (ctx=0x807f128, length=4294916861, 
>    data=0x808effc "") at sha256.c:92
>#2  0x003b336d in nettle_hmac_sha256_update (ctx=0x807f050, length=4294967280, 
>    data=0x8082b09 '\017' <repeats 16 times>) at hmac-sha256.c:43
>#3  0x0021a749 in wrap_nettle_hmac_update (_ctx=0x807f050, text=0x8082b09, 
>    textsize=4294967280) at mac.c:231
>#4  0x00158233 in _gnutls_hmac (handle=0x807ef9c, text=0x8082b09, 
>    textlen=4294967280) at ./gnutls_hash_int.h:73
>#5  0x00158b35 in _gnutls_auth_cipher_add_auth (handle=0x807ef78, 
>    text=0x8082b09, textlen=-16) at gnutls_cipher_int.c:190
>#6  0x001473de in ciphertext_to_compressed (session=0x807d810, 
>    ciphertext=0xbfffe8a4, compress_data=0x8083da4 "", compress_size=16384, 
>    type=22 '\026', params=0x807ed48, sequence=0x807efcc)
>    at gnutls_cipher.c:587
>#7  0x00145cdc in _gnutls_decrypt (session=0x807d810, 
>    ciphertext=0x8082af9 "\252\257C/7\301\362\352h|d\275#\312\027\312", '\017' <repeats 16 times>, ciphertext_size=32, data=0x8083da4 "", max_data_size=16384, 
>    type=GNUTLS_HANDSHAKE, params=0x807ed48, sequence=0x807efcc)
>    at gnutls_cipher.c:159
>...
>(gdb) 
>
>The segmentation fault appears as follows in Valgrind Memcheck:
>
>==29586== Invalid read of size 1
>==29586==    at 0x40274B9: memcpy (mc_replace_strmem.c:497)
>==29586==    by 0x42BC5A6: nettle_sha256_update (sha256.c:92)
>==29586==    by 0x42B636C: nettle_hmac_sha256_update (hmac-sha256.c:43)
>==29586==    by 0x411C748: wrap_nettle_hmac_update (mac.c:231)
>==29586==    by 0x405A232: _gnutls_hmac (gnutls_hash_int.h:73)
>==29586==    by 0x405AB34: _gnutls_auth_cipher_add_auth (gnutls_cipher_int.c:190)
>==29586==    by 0x40493DD: ciphertext_to_compressed (gnutls_cipher.c:587)
>==29586==    by 0x4047CDB: _gnutls_decrypt (gnutls_cipher.c:159)
>...
>==29586==  Address 0x4464411 is 0 bytes after a block of size 89 alloc'd
>==29586==    at 0x4024F12: calloc (vg_replace_malloc.c:467)
>==29586==    by 0x4049AE4: _mbuffer_alloc (gnutls_mbuffers.c:288)
>==29586==    by 0x4049C49: _mbuffer_linearize (gnutls_mbuffers.c:349)
>==29586==    by 0x40462FB: _gnutls_recv_in_buffers (gnutls_record.c:996)
>==29586==    by 0x404D01C: _gnutls_handshake_io_recv_int (gnutls_buffers.c:1174)
>==29586==    by 0x4050383: _gnutls_recv_handshake (gnutls_handshake.c:1260)
>...
>==29586== Invalid read of size 1
>...
>==29586==  Address 0x4464412 is 1 bytes after a block of size 89 alloc'd
>...
>==29586== Process terminating with default action of signal 11 (SIGSEGV)
>==29586==  Access not within mapped region at address 0x4779000
>==29586==    at 0x42BC946: _nettle_sha256_compress (sha256-compress.c:111)
>==29586==    by 0x42BC61A: nettle_sha256_update (sha256.c:92)
>==29586==    by 0x42B636C: nettle_hmac_sha256_update (hmac-sha256.c:43)
>==29586==    by 0x411C748: wrap_nettle_hmac_update (mac.c:231)
>==29586==    by 0x405A232: _gnutls_hmac (gnutls_hash_int.h:73)
>==29586==    by 0x405AB34: _gnutls_auth_cipher_add_auth (gnutls_cipher_int.c:190)
>==29586==    by 0x40493DD: ciphertext_to_compressed (gnutls_cipher.c:587)
>...
>Segmentation fault
>
>Details for ASN.1 length decoding vulnerability in Libtasn1 [MU-201202-02]:
>
>Various functions using the ASN.1 length decoding logic in Libtasn1 were 
>incorrectly assuming that the return value from asn1_get_length_der is always 
>less than the length of the enclosing ASN.1 structure, which is only true for 
>valid structures and not for intentionally corrupt or otherwise buggy 
>structures.
>
>Here is an example of unsafe asn1_get_length_der usage from 
>lib/minitasn1/decoding.c, in the asn1_der_decoding function:
>
>0812    asn1_retCode
>0813    asn1_der_decoding (ASN1_TYPE * element, const void *ider, int len,
>0814                       char *errorDescription)
>0815    {
>...
>1033                case TYPE_ENUMERATED:
>1034                  len2 =
>1035                    asn1_get_length_der (der + counter, len - counter, &len3);
>1036                  if (len2 < 0)
>1037                    return ASN1_DER_ERROR;
>1038                  if (len2 + len3 > len - counter)
>1039                    return ASN1_DER_ERROR;
>1040                  _asn1_set_value (p, der + counter, len3 + len2);
>1041                  counter += len3 + len2;
>1042                  move = RIGHT;
>1043                  break;
>
>The above call to asn1_get_length_der was returning an impossibly large value 
>of 2GB when the Mu analyzer generated corrupt lengths fields for versions, 
>serial numbers, public key info, and signature structures in X.509 client 
>certificates, but this could happen in any use of Libtasn1 that is relying 
>upon asn1_get_length_der, not just SSL, TLS, or GnuTLS.
>
>The asn1_der_decoding function failed to check for cases when 
>asn1_get_length_der returned a length larger than the enclosing structure's 
>(void* ider) own length (int len).
>
>When _asn1_set_value was called anyway, it contained a memcpy operation which 
>assumed the arguments are valid, which tried copy 2GB of memory, leading to a 
>heap corruption vulnerability.
>
>Simon Josefsson, Libtasn1 maintainer, described the patch as follows: "the 
>real bug was not in asn1_get_length_der() even if that is the function we 
>patch[ed]. The callers of that function that did not check that the return 
>values are sane were buggy. However, instead of fixing all callers, ... we 
>went for the simpler solution to let the function return an error for a 
>situation that is unlikely to occur without malicious interaction or data 
>corruption."
>
>The asn1_der_decoding function shown above is now safe, because 
>asn1_get_length_der was updated to "[return] -4 when the decoded length value 
>plus @len would exceed @der_len," so asn1_der_decoding returns ASN1_DER_ERROR 
>before it can call _asn1_set_value to trigger the segmentation fault.
>
>Abbreviated GDB Backtrace after the segmentation fault:
>
>(gdb) bt
>#0  __memcpy_ia32 () at ../sysdeps/i386/i686/multiarch/../memcpy.S:75
>#1  0x00000001 in ?? ()
>#2  0x0020eadc in _asn1_set_value (node=0x807ff50, value=0x807ed5c, 
>    len=2147483652) at parser_aux.c:228
>#3  0x0020a646 in asn1_der_decoding (element=0x8078000, ider=0x807ed4e, 
>    len=687, errorDescription=0x0) at decoding.c:1036
>#4  0x001bc7da in gnutls_x509_crt_import (cert=0x8078000, data=0xbfffeae8, 
>    format=GNUTLS_X509_FMT_DER) at x509.c:226
>#5  0x00176d16 in gnutls_pcert_import_x509_raw (pcert=0x807d610, 
>    cert=0xbfffeae8, format=GNUTLS_X509_FMT_DER, flags=0) at gnutls_pcert.c:201
>...
>(gdb) 
>
>Response / Solution:
>
>TLS record handling vulnerability in GnuTLS [MU-201202-01] is fixed in GnuTLS 
>3.0.15. For more details, see 
>http://article.gmane.org/gmane.comp.encryption.gpg.gnutls.devel/5912 .
>
>ASN.1 length decoding vulnerability in Libtasn1 [MU-201202-02] is fixed in 
>Libtasn1 2.12 and GnuTLS 3.0.16. For more details, see 
>http://lists.gnu.org/archive/html/help-libtasn1/2012-03/msg00000.html and 
>http://article.gmane.org/gmane.comp.encryption.gpg.gnutls.devel/5932 .
>
>History:
>
>Mon, 27 Feb 2012 14:13:45 -0800: TLS Record handling issue reported.
>Tue, 28 Feb 2012 10:29:46 +0100: TLS Record handling patch created.
>Fri, 02 Mar 2012 18:42:05 +0000: GnuTLS 3.0.15 release announced.
>Fri, 02 Mar 2012 14:04:31 -0800: ASN.1 length decoding issue reported.
>Wed, 14 Mar 2012 01:04:36 +0100: ASN.1 length decoding patch created.
>Mon, 19 Mar 2012 10:57:42 +0100: Libtasn1 2.12 release announced.
>Tue, 20 Mar 2012 23:40:00 +0000: Advisory released to the public.
>
>See also:
>
>http://article.gmane.org/gmane.comp.encryption.gpg.gnutls.devel/5912
>http://article.gmane.org/gmane.comp.encryption.gpg.gnutls.devel/5932
>http://lists.gnu.org/archive/html/help-libtasn1/2012-03/msg00000.html
>http://git.savannah.gnu.org/gitweb/?p=gnutls.git;a=commitdiff;h=b495740f2ff66550ca9395b3fda3ea32c3acb185
>http://git.savannah.gnu.org/gitweb/?p=libtasn1.git;a=commitdiff;h=6e534bf4fb3144be51c928ed3efcf9c36055c9c7
>
>Credit:
>
>These vulnerabilities were discovered by Matthew Hall <mhall@mudynamics.com>, 
>Senior Network Protocol Software Engineer at Mu Dynamics, via code inspection 
>and protocol fuzzing using a Mu 4000 security analyzer.
>
>http://blog.mudynamics.com/wp-content/uploads/2012/03/pgpkey.txt
>
>Mu Dynamics is the leading provider of solutions ensuring the performance and 
>security of both applications and network infrastructure. The company's 
>innovative solutions enable customers to confidently meet the challenges posed 
>by today's rapidly changing networks. This includes the ever-growing number of 
>applications and devices on the network, and the swift transition to mobile, 
>virtual and cloud environments. Hundreds of service providers, enterprises, 
>application developers and network equipment manufacturers count on its 
>purpose-built solutions, like Mu Studio and Blitz, to ensure their 
>applications and networks are scalable and secure. Mu Dynamics is 
>headquartered in Sunnyvale, California.
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