From e6ae703ae597d798e310368d52b8f38ee11c6a73 Mon Sep 17 00:00:00 2001 From: Greg Hudson Date: Thu, 19 Jun 2014 13:49:16 -0400 Subject: [PATCH] Handle invalid RFC 1964 tokens [CVE-2014-4341...] Detect the following cases which would otherwise cause invalid memory accesses and/or integer underflow: * An RFC 1964 token being processed by an RFC 4121-only context [CVE-2014-4342] * A header with fewer than 22 bytes after the token ID or an incomplete checksum [CVE-2014-4341 CVE-2014-4342] * A ciphertext shorter than the confounder [CVE-2014-4341] * A declared padding length longer than the plaintext [CVE-2014-4341] If we detect a bad pad byte, continue on to compute the checksum to avoid creating a padding oracle, but treat the checksum as invalid even if it compares equal. CVE-2014-4341: In MIT krb5, an unauthenticated remote attacker with the ability to inject packets into a legitimately established GSSAPI application session can cause a program crash due to invalid memory references when attempting to read beyond the end of a buffer. CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:P/E:POC/RL:OF/RC:C CVE-2014-4342: In MIT krb5 releases krb5-1.7 and later, an unauthenticated remote attacker with the ability to inject packets into a legitimately established GSSAPI application session can cause a program crash due to invalid memory references when reading beyond the end of a buffer or by causing a null pointer dereference. CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:P/E:POC/RL:OF/RC:C [tlyu@mit.edu: CVE summaries, CVSS] (cherry picked from commit fb99962cbd063ac04c9a9d2cc7c75eab73f3533d) ticket: 7949 version_fixed: 1.12.2 status: resolved --- src/lib/gssapi/krb5/k5unseal.c | 41 +++++++++++++++++++++++++------ src/lib/gssapi/krb5/k5unsealiov.c | 9 ++++++- 2 files changed, 41 insertions(+), 9 deletions(-) diff --git a/src/lib/gssapi/krb5/k5unseal.c b/src/lib/gssapi/krb5/k5unseal.c index ca21d43a959..b65c83ca7ca 100644 --- a/src/lib/gssapi/krb5/k5unseal.c +++ b/src/lib/gssapi/krb5/k5unseal.c @@ -74,6 +74,7 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer, int conflen = 0; int signalg; int sealalg; + int bad_pad = 0; gss_buffer_desc token; krb5_checksum cksum; krb5_checksum md5cksum; @@ -86,6 +87,7 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer, krb5_ui_4 seqnum; OM_uint32 retval; size_t sumlen; + size_t padlen; krb5_keyusage sign_usage = KG_USAGE_SIGN; if (toktype == KG_TOK_SEAL_MSG) { @@ -93,18 +95,23 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer, message_buffer->value = NULL; } - /* get the sign and seal algorithms */ - - signalg = ptr[0] + (ptr[1]<<8); - sealalg = ptr[2] + (ptr[3]<<8); - /* Sanity checks */ - if ((ptr[4] != 0xff) || (ptr[5] != 0xff)) { + if (ctx->seq == NULL) { + /* ctx was established using a newer enctype, and cannot process RFC + * 1964 tokens. */ + *minor_status = 0; + return GSS_S_DEFECTIVE_TOKEN; + } + + if ((bodysize < 22) || (ptr[4] != 0xff) || (ptr[5] != 0xff)) { *minor_status = 0; return GSS_S_DEFECTIVE_TOKEN; } + signalg = ptr[0] + (ptr[1]<<8); + sealalg = ptr[2] + (ptr[3]<<8); + if ((toktype != KG_TOK_SEAL_MSG) && (sealalg != 0xffff)) { *minor_status = 0; @@ -153,6 +160,11 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer, return GSS_S_DEFECTIVE_TOKEN; } + if ((size_t)bodysize < 14 + cksum_len) { + *minor_status = 0; + return GSS_S_DEFECTIVE_TOKEN; + } + /* get the token parameters */ if ((code = kg_get_seq_num(context, ctx->seq, ptr+14, ptr+6, &direction, @@ -207,7 +219,20 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer, plainlen = tmsglen; conflen = kg_confounder_size(context, ctx->enc->keyblock.enctype); - token.length = tmsglen - conflen - plain[tmsglen-1]; + if (tmsglen < conflen) { + if (sealalg != 0xffff) + xfree(plain); + *minor_status = 0; + return(GSS_S_DEFECTIVE_TOKEN); + } + padlen = plain[tmsglen - 1]; + if (tmsglen - conflen < padlen) { + /* Don't error out yet, to avoid padding oracle attacks. We will + * treat this as a checksum failure later on. */ + padlen = 0; + bad_pad = 1; + } + token.length = tmsglen - conflen - padlen; if (token.length) { if ((token.value = (void *) gssalloc_malloc(token.length)) == NULL) { @@ -403,7 +428,7 @@ kg_unseal_v1(context, minor_status, ctx, ptr, bodysize, message_buffer, /* compare the computed checksum against the transmitted checksum */ - if (code) { + if (code || bad_pad) { if (toktype == KG_TOK_SEAL_MSG) gssalloc_free(token.value); *minor_status = 0; diff --git a/src/lib/gssapi/krb5/k5unsealiov.c b/src/lib/gssapi/krb5/k5unsealiov.c index e34bda4754b..8d6a2dacffb 100644 --- a/src/lib/gssapi/krb5/k5unsealiov.c +++ b/src/lib/gssapi/krb5/k5unsealiov.c @@ -69,7 +69,14 @@ kg_unseal_v1_iov(krb5_context context, return GSS_S_DEFECTIVE_TOKEN; } - if (header->buffer.length < token_wrapper_len + 14) { + if (ctx->seq == NULL) { + /* ctx was established using a newer enctype, and cannot process RFC + * 1964 tokens. */ + *minor_status = 0; + return GSS_S_DEFECTIVE_TOKEN; + } + + if (header->buffer.length < token_wrapper_len + 22) { *minor_status = 0; return GSS_S_DEFECTIVE_TOKEN; }