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| Code Block | ||||
|---|---|---|---|---|
| ||||
int dtls1_process_heartbeat(SSL *s) {
unsigned char *p = &s->s3->rrec.data[0], *pl;
unsigned short hbtype;
unsigned int payload;
unsigned int padding = 16; /* Use minimum padding */
/* Read type and payload length first */
hbtype = *p++;
n2s(p, payload);
pl = p;
//* ... More code ... */
if (hbtype == TLS1_HB_REQUEST) {
unsigned char *buffer, *bp;
int r;
/* Allocate memory for the response, size is 1 byte
* message type, plus 2 bytes payload length, plus
* payload, plus padding
*/
buffer = OPENSSL_malloc(1 + 2 + payload + padding);
bp = buffer;
/* Enter response type, length and copy payload */
*bp++ = TLS1_HB_RESPONSE;
s2n(payload, bp);
memcpy(bp, pl, payload);
//* ... More code ... */
}
//* ... More code ... */
} |
This code processes a 'heartbeat' packet from a client. The p pointer, along with payload and p1 contain data from this packet. The code allocates a buffer sufficient to contain payload bytes, with some overhead, and copies payload bytes starting at p1 into this buffer, and sends it to the client. Notably absent are any checks that payload actually indicates the correct size of the memory. Because an attacker can specify an arbitrary value for payload, she can cause this routine to read and return memory beyond the block allocated to p.
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Compliant Solution (Heartbleed)
OpenSSL version 1.0.1g contains the following patch, which guarantees that payload is within a valid range:
| Code Block | ||||
|---|---|---|---|---|
| ||||
int dtls1_process_heartbeat(SSL *s) {
unsigned char *p = &s->s3->rrec.data[0], *pl;
unsigned short hbtype;
unsigned int payload;
unsigned int padding = 16; /* Use minimum padding */
//* ... More code ... */
/* Read type and payload length first */
if (1 + 2 + 16 > s->s3->rrec.length)
return 0; /* silently discard */
hbtype = *p++;
n2s(p, payload);
if (1 + 2 + payload + 16 > s->s3->rrec.length)
return 0; /* silently discard per RFC 6520 se
pl = p;
//* ... More code ... */
if (hbtype == TLS1_HB_REQUEST) {
unsigned char *buffer, *bp;
int r;
/* Allocate memory for the response, size is 1 byte
* message type, plus 2 bytes payload length, plus
* payload, plus padding
*/
buffer = OPENSSL_malloc(1 + 2 + payload + padding);
bp = buffer;
/* Enter response type, length and copy payload */
*bp++ = TLS1_HB_RESPONSE;
s2n(payload, bp);
memcpy(bp, pl, payload);
//* ... More code ... */
}
//* ... More code ... */
} |
Risk Assessment
Failing to enforce the limits on integer values can result in a denial-of-service attack.
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