Full Report
This year marks a special anniversary for us at SensePost in that we’ve been training at BlackHat for over a decade now. To celebrate this, we thought we’d give away a free ticket to any of our courses on offer at this year’s BlackHat Briefings in Las Vegas. With data breaches happening almost on a monthly basis these days, everyone is turning to encryption in order to protect their information. Bob, a rather tech-savvy gentleman, works for a FTSE 100 company and they’ve written their own secure message implementation. You’ve been tasked to perform a penetration test and noticed that after compromising their shared document server, an internal web application leaked the source code used by the company for the client and the server.
Analysis Summary
# Incident Report: Custom Encryption Scheme Compromise via Source Code Leak
## Executive Summary
The incident involves a penetration tester gaining access to a FTSE 100 company's internal systems, specifically compromising a shared document server. This led to the subsequent leak of the source code for the company's proprietary, supposedly secure messaging implementation (client and server sides). The leaked source code, combined with network traffic analysis, allowed the tester to deduce the length and character set of the shared secret key, ultimately enabling the decryption of communications.
## Incident Details
- Discovery Date: June 14, 2012 (Date of publication of the challenge/report findings)
- Incident Date: Not explicitly stated, but occurred prior to/during the penetration test.
- Affected Organization: FTSE 100 Company (Unspecified)
- Sector: Finance/Technology Services (Based on FTSE 100 designation)
- Geography: Las Vegas (Location of the associated BlackHat Briefings, contextually relevant)
## Timeline of Events
### Initial Access
- Date/Time: Prior to discovery (During penetration test)
- Vector: Compromise of the shared document server.
- Details: An unspecified entry point was used to gain access to the internal shared document server.
### Lateral Movement
- Date/Time: Post Initial Access
- Vector: Implicitly, the compromise of the server provided a beachhead.
- Details: The successful compromise of the document server allowed the attacker to locate and access the source code files for the client and server applications.
### Data Exfiltration/Impact
- Date/Time: Post Source Code Leak
- Vector: Leakage/Download of source code and unauthorized monitoring of network traffic.
- Details: The source code for the client/server secure message implementation was exposed via an internal web application. Authentication protocol traffic (PCAP) was intercepted, and combined with the source code, the shared secret and encryption key ($k_c$) were calculated, breaking the encryption.
### Detection & Response
- Date/Time: Post-compromise (Challenge published June 14, 2012)
- Vector: External challenge/reporting structure (SensePost contest).
- Details: The client/server developers were informed but maintained the encryption was unbreakable. The resolution involved a third party (the contest winner) proving the encryption method weak by recovering the secret key. The organization's response actions are not explicitly detailed beyond the assertion that communication was subsequently decrypted.
## Attack Methodology
- Initial Access: Compromise of a shared document server.
- Persistence: Not explicitly detailed, though access was maintained long enough to gather source code.
- Privilege Escalation: Not explicitly detailed.
- Defense Evasion: The proprietary encryption mechanism was the primary defense, which was bypassed via source code review rather than cryptographic attack alone.
- Credential Access: Bob's password history was observed (which indirectly provided information on the shared secret/key constraints).
- Discovery: Analysis of intercepted authentication protocol traffic (PCAP) and review of obtained client/server source files.
- Lateral Movement: Gaining access to the internal web application hosting the source code from the document server foothold.
- Collection: Interception of network traffic ($PCAP$) and procurement of source code files.
- Exfiltration: Source code files were leaked/downloaded; network credentials/keys were calculated and used to decrypt communications.
- Impact: Loss of confidentiality for encrypted communications due to cryptographic failure revealed by source code exposure.
## Impact Assessment
- Financial: Not specified (Potential high cost due to proprietary implementation failure).
- Data Breach: Confidential communications (encrypted messages) were rendered readable. The sensitivity of the messages themselves is unknown.
- Operational: Potential disruption due to immediate need to overhaul the security infrastructure.
- Reputational: Significant due to proprietary, touted-as-secure software being immediately broken by analyzing leaked source code.
## Indicators of Compromise
- Network Indicators: PCAP file showing authentication protocol traffic (contains traffic used to reverse-engineer key length/constraints).
- File Indicators: Source files for client/server secure message implementation.
- Behavioral Indicators: Successful interception of authentication traffic preceding an unencrypted session.
## Response Actions
- Containment measures: Not specified, but implied immediate need to patch/replace the vulnerable application upon realizing the method was broken.
- Eradication steps: Not specified.
- Recovery actions: Not specified, but recovery would necessitate replacing the entire custom messaging protocol.
## Lessons Learned
- **Proprietary Security is Insufficient:** Relying on custom, "roll-your-own" encryption implementations without rigorous, external review is extremely dangerous, especially when source code can be leaked.
- **Defense in Depth Failure:** Compromise of low-security assets (shared document server) led directly to the theft of high-value assets (source code), exposing cryptographic weaknesses.
- **Key Constraints Leak Information:** Observing patterns in user behavior (password history) combined with known implementation constraints (7-character, alpha-numeric, no upper-case secret key) drastically reduced the attacker's attack surface.
## Recommendations
- Immediately review and replace the proprietary secure message implementation with industry-standard, peer-reviewed cryptographic libraries and protocols.
- Segment and strictly control access to document servers and repositories containing application source code.
- Implement two-factor authentication or stronger credential management regardless of the encryption layer used for communication.