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From Software Bugs to Security Vulnerabilities

  • Software bugs cause damages:
    • Therac-25 radiation overdose.
    • Ariane-5 rocket disaster.
    • Northeastern blackout in 2003.
    • Security vulnerablilities.
  • Program analysis can prevent bugs.
  • Common Vulnerabilities and Exposures (CVE)
    • Catalog security vulnerablilities.
    • CVE ID number.
    • Description.
    • References.

Case Study 1: OpenSSL Heatbleed Bug CVE-2014-0160​

  • OpenSSL used to secure communication over computer networks.
  • Heartbleed eavesdropped on SSL/TLS encryption protocol.
  • Bug in TLS "heartbeat extension", a protocol to check if server is alive.
  • Server sends back positive acknowledgement by returning copy of received data.
  • Code for processing incoming message: 
    hbtype = *p++;
    n2s(p, payload);        // write two bytes from ‘p’ into ‘payload’
    pl = p;  // ‘pl’ now points to contents of payload
  • Code for constructing reply: 
    *bp++ = TLS1_HB_RESPONSE;
    n2s(payload, bp);       // write two bytes from ‘payload’ into ‘bp’ 
    memcpy(bp, pl, payload) // copy ‘payload’ bytes from ‘pl’ to ‘bp’
  • Send a message with small payload data but specify different longer length, memcpy will read more data.
  • Needs bounds-checking to prevent this: 
    hbtype = *p++;
    n2s(p, payload);
    if (1 + 2 + payload + 16 > ...) // “...” is received message’s length
    	return 0;  // silently discard per RFC 6520 sec. 4
    pl = p;
  • Automatically discover using dynamic/static analysis.
  • Dynamic approach: use LibFuzzer, Address Sanitizer. Fuzzer constructs abnormal inputs. Sanitizer errors out memcpy.
  • Static approach: use Coverity, information-flow/taint-tracking analysis.

Case Study 2: Apple's "Goto Fail" Bug CVE-2014-1266​

  • Capture and modify data in sessions secured by SSL/TLS.
  • Bug in function that verifies SSL key exchange. 
    static OSStatus SSLVerifySignedServerKeyExchange( ... ) {
    ...
    if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
    	goto fail;
    	goto fail;
    ...
    err = sslRawVerify( ... );
    ...
    fail:
    	SSLFreeBuffer(&signedHashes);
    	SSLFreeBuffer(&hashCtx);
    	return err;
    }
  • Second goto fail is unconditional.
  • sslRawVerify is bypassed.
  • SSLVerifySignedServerKeyExchange function returns successful even when it's not.
  • Attacker can do man-in-the-middle attack.
  • Automatically detect bug using static analysis.
  • Unreachable code analysis: can reveal portion of code unreachable after the second goto statement.

Case Study 3: VLC Media Player Dependency Bug CVE-2019-13615​

  • Heap-based buffer over-read in EBML component that parses media types.
  • Enabled remote code execution and access user's machine if user opened a malicious file.
  • Bug in: 
    EbmlElement* EbmlElement::FindNextElement( ... ) {
    ...
    do {
    	...
    	if (DataStream.read(&PossibleIdNSize[ReadIndex++], 1) == 0) {
    		return NULL;
    	}
    	ReadSize++;
    	...
    while (...);
    ...
    }
  • Bound-check missing before reading, attacker can read beyond bounds. Fix: 
    EbmlElement * EbmlElement::FindNextElement(...) {
    	...
    	if (MaxDataSize <= ReadSize)
    		break;
    	if (DataStream.read(&PossibleIdNSize[ReadIndex++], 1) == 0) {
    		return NULL;
    	}
    	ReadSize++;
    	...
    }
  • Use fuzzing to automatically detect this.