A capture-replay flaw exists when the design of the software
makes it possible for a malicious user to sniff network traffic and bypass
authentication by replaying it to the server in question to the same effect as
the original message (or with minor changes).
Extended Description
Capture-replay attacks are common and can be difficult to defeat without
cryptography. They are a subset of network injection attacks that rely on
observing previously-sent valid commands, then changing them slightly if
necessary and resending the same commands to the server.
Time of Introduction
Architecture and Design
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Authorization
Messages sent with a capture-relay attack allow access to resources
which are not otherwise accessible without proper authentication.
Likelihood of Exploit
High
Demonstrative Examples
Example 1
C and C++
unsigned char *simple_digest(char *alg,char *buf,unsigned int len,
int *olen) {
const EVP_MD *m; EVP_MD_CTX ctx;
unsigned char *ret;
OpenSSL_add_all_digests();
if (!(m = EVP_get_digestbyname(alg))) return NULL;
if (!(ret = (unsigned char*)malloc(EVP_MAX_MD_SIZE))) return
NULL;
product authentication succeeds if user-provided
MD5 hash matches the hash in its database; this can be subjected to replay
attacks.
Potential Mitigations
Phase
Description
Architecture and Design
Utilize some sequence or time stamping functionality along with a
checksum which takes this into account in order to ensure that messages
can be parsed only once.
Architecture and Design
Since any attacker who can listen to traffic can see sequence
numbers, it is necessary to sign messages with some kind of cryptography
to ensure that sequence numbers are not simply doctored along with
content.
Description
