CVE-2017-15088 (published 2017-11-23T17:29Z)

plugins/preauth/pkinit/pkinit_crypto_openssl.c in MIT Kerberos 5 (aka krb5) through 1.15.2 mishandles Distinguished Name (DN) fields, which allows remote attackers to execute arbitrary code or cause a denial of service (buffer overflow and application crash) in situations involving untrusted X.509 data, related to the get_matching_data and X509_NAME_oneline_ex functions. NOTE: this has security relevance only in use cases outside of the MIT Kerberos distribution, e.g., the use of get_matching_data in KDC certauth plugin code that is specific to Red Hat.

Severity: HIGH
CVSS v2 base score: 7.5 (AV:N/AC:L/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 9.8, CRITICAL (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-119
cwe_name: Improper Restriction of Operations within the Bounds of a Memory Buffer
description: The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
extended_description: 
            Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.
         
         

Fix information:
repo_url: https://github.com/krb5/krb5
commit_details: repo_url: https://github.com/krb5/krb5
author: Greg Hudson
author_date: 2017-10-17 18:50:15-04:00
msg: Fix PKINIT cert matching data construction

Rewrite X509_NAME_oneline_ex() and its call sites to use dynamic
allocation and to perform proper error checking.

ticket: 8617
target_version: 1.16
target_version: 1.15-next
target_version: 1.14-next
tags: pullup
repository: repo_url: https://github.com/krb5/krb5
repo_name: krb5/krb5
description: mirror of MIT krb5 repository
repo_language: C
owner: krb5
file_changes: filename: pkinit_crypto_openssl.c
change_type: ModificationType.MODIFY
diff: @@ -5002,33 +5002,29 @@ out:
     return retval;
 }
 
-/*
- * Return a string format of an X509_NAME in buf where
- * size is an in/out parameter.  On input it is the size
- * of the buffer, and on output it is the actual length
- * of the name.
- * If buf is NULL, returns the length req'd to hold name
- */
-static char *
-X509_NAME_oneline_ex(X509_NAME * a,
-                     char *buf,
-                     unsigned int *size,
-                     unsigned long flag)
+static krb5_error_code
+rfc2253_name(X509_NAME *name, char **str_out)
 {
-    BIO *out = NULL;
+    BIO *b = NULL;
+    char *str;
 
-    out = BIO_new(BIO_s_mem ());
-    if (X509_NAME_print_ex(out, a, 0, flag) > 0) {
-        if (buf != NULL && (*size) >  (unsigned int) BIO_number_written(out)) {
-            memset(buf, 0, *size);
-            BIO_read(out, buf, (int) BIO_number_written(out));
-        }
-        else {
-            *size = BIO_number_written(out);
-        }
-    }
-    BIO_free(out);
-    return (buf);
+    *str_out = NULL;
+    b = BIO_new(BIO_s_mem());
+    if (b == NULL)
+        return ENOMEM;
+    if (X509_NAME_print_ex(b, name, 0, XN_FLAG_SEP_COMMA_PLUS) < 0)
+        goto error;
+    str = calloc(BIO_number_written(b) + 1, 1);
+    if (str == NULL)
+        goto error;
+    BIO_read(b, str, BIO_number_written(b));
+    BIO_free(b);
+    *str_out = str;
+    return 0;
+
+error:
+    BIO_free(b);
+    return ENOMEM;
 }
 
 /*
@@ -5094,8 +5090,6 @@ get_matching_data(krb5_context context,
     pkinit_cert_matching_data *md = NULL;
     krb5_principal *pkinit_sans = NULL, *upn_sans = NULL;
     size_t i, j;
-    char buf[DN_BUF_LEN];
-    unsigned int bufsize = sizeof(buf);
 
     *md_out = NULL;
 
@@ -5103,23 +5097,12 @@ get_matching_data(krb5_context context,
     if (md == NULL)
         goto cleanup;
 
-    /* Get the subject name (in rfc2253 format). */
-    X509_NAME_oneline_ex(X509_get_subject_name(cert), buf, &bufsize,
-                         XN_FLAG_SEP_COMMA_PLUS);
-    md->subject_dn = strdup(buf);
-    if (md->subject_dn == NULL) {
-        ret = ENOMEM;
+    ret = rfc2253_name(X509_get_subject_name(cert), &md->subject_dn);
+    if (ret)
         goto cleanup;
-    }
-
-    /* Get the issuer name (in rfc2253 format). */
-    X509_NAME_oneline_ex(X509_get_issuer_name(cert), buf, &bufsize,
-                         XN_FLAG_SEP_COMMA_PLUS);
-    md->issuer_dn = strdup(buf);
-    if (md->issuer_dn == NULL) {
-        ret = ENOMEM;
+    ret = rfc2253_name(X509_get_issuer_name(cert), &md->issuer_dn);
+    if (ret)
         goto cleanup;
-    }
 
     /* Get the SAN data. */
     ret = crypto_retrieve_X509_sans(context, plg_cryptoctx, req_cryptoctx,

programming_language: C