Adobe Acrobat - CraftedSignal Threat Feedhttps://feed.craftedsignal.io/products/adobe-acrobat/Trending threats, MITRE ATT&CK coverage, and detection metadata. Fed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioWed, 03 Jan 2024 12:00:00 +0000Suspicious PDF Reader Child Process Executionhttps://feed.craftedsignal.io/briefs/2024-01-suspicious-pdf-child-process/Wed, 03 Jan 2024 12:00:00 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2024-01-suspicious-pdf-child-process/Adversaries may exploit vulnerabilities in PDF reader applications or use social engineering to execute malicious commands, often spawning system utilities for discovery or defense evasion purposes.Attackers frequently target PDF reader applications due to their widespread use and complex codebase, providing multiple avenues for exploitation. These exploits can range from memory corruption vulnerabilities to logic flaws that allow arbitrary code execution. Social engineering is also a common tactic, where users are tricked into opening malicious PDF files that trigger the execution of embedded scripts or commands. The spawned processes often include system utilities used for reconnaissance or persistence. This technique is used for initial access, defense evasion, and discovery within the targeted environment. The detection rule provided by Elastic identifies suspicious child processes of PDF reader applications.

Attack Chain

  1. A user receives a spearphishing email with a malicious PDF attachment (T1566.001).
  2. The user opens the PDF file using a vulnerable PDF reader application (e.g., Acrobat Reader, Foxit Reader).
  3. The PDF file exploits a vulnerability in the PDF reader, triggering the execution of embedded JavaScript or shell commands (T1203, T1204.002).
  4. The exploited PDF reader process (AcroRd32.exe, Acrobat.exe, FoxitPhantomPDF.exe, FoxitReader.exe) spawns a suspicious child process such as cmd.exe or powershell.exe (T1059.001).
  5. The spawned process executes discovery commands (e.g., whoami.exe, systeminfo.exe, net.exe, ipconfig.exe) to gather information about the system and network (T1082, T1016, T1033, T1057).
  6. The attacker may use system binary proxy execution (T1218) techniques by invoking utilities such as mshta.exe, regsvr32.exe, or installutil.exe to execute malicious code.
  7. The attacker establishes persistence on the system, potentially using scheduled tasks (schtasks.exe) or registry modifications (reg.exe).
  8. The attacker moves laterally within the network, escalating privileges, and exfiltrating sensitive data, or deploying ransomware.

Impact

Compromised systems can lead to data theft, system disruption, and further propagation of the attack within the network. Successful exploitation of PDF reader vulnerabilities can provide attackers with initial access to the target environment, potentially impacting hundreds or thousands of machines across an organization. The impact can range from minor data breaches to full-scale ransomware deployment, depending on the attacker's objectives.

Recommendation

  • Deploy the Sigma rule "Suspicious PDF Reader Child Process" to your SIEM to detect suspicious child processes spawned by PDF readers.
  • Enable process creation logging, specifically monitoring for AcroRd32.exe, Acrobat.exe, FoxitPhantomPDF.exe, and FoxitReader.exe spawning command-line interpreters or other suspicious utilities.
  • Ensure PDF reader applications are patched to the latest versions to mitigate known vulnerabilities.
  • Implement email filtering to block suspicious attachments and educate users about the risks of opening unsolicited PDF files.
  • Monitor network connections originating from PDF reader applications for unusual outbound traffic.
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