A severe vulnerability in Apache Commons Text—a ubiquitous Java library used for string manipulation—has ignited urgent patching efforts across the industry. Tracked as CVE-2022-42889 and nicknamed Text4Shell, the flaw allows attackers to execute arbitrary code remotely by crafting malicious input strings that exploit the library's insecure interpolation feature.

How the Exploit Works

The vulnerability resides in the StringSubstitutor class, which processes ${} placeholders to dynamically resolve variables. When configured with dangerous interpolators like script, dns, or url, attackers can inject payloads that trigger Java script engine execution:

String payload = "${script:javascript:java.lang.Runtime.getRuntime().exec('calc')}";
StringSubstitutor.replace(payload); // Executes calculator app

Unlike Log4Shell (which impacted logging), Text4Shell requires applications to explicitly use StringSubstitutor with vulnerable configurations—a narrower but still pervasive attack surface. Cloud services, web apps, and enterprise software using Commons Text versions 1.5–1.9 are at risk.

Key Differences from Log4Shell

  1. Exploitation Complexity: Text4Shell demands specific library configurations for exploitability, whereas Log4Shell was exploitable by default.
  2. Attack Vector: Requires input passed directly to StringSubstitutor (e.g., form fields, API parameters), not merely logged messages.
  3. Mitigation Simplicity: Setting org.apache.commons.text.StringSubstitutor.DEFAULT_ESCAPE to disable ${} parsing offers temporary hardening.

"While less catastrophic than Log4Shell, Text4Shell still threatens any system processing untrusted input with Commons Text," warns Tenable security researcher Satnam Narang. "Developers must patch to Commons Text 1.10.0, which removes dangerous interpolators by default."

Industry Response

  • Apache released a patch within 48 hours of disclosure, removing high-risk interpolators.
  • AWS, VMware, and Cisco issued advisories confirming investigations into affected products.
  • Exploit attempts surged within 72 hours, per GreyNoise telemetry, targeting exposed APIs and web interfaces.

Action Plan for Teams

  1. Scan dependencies for Commons Text versions 1.5–1.9
  2. Upgrade to 1.10.0+ or apply vendor patches immediately
  3. Audit code for StringSubstitutor usage with untrusted inputs
  4. Monitor for anomalous process executions (e.g., cmd.exe, bash spawns)

The incident underscores Java's persistent struggle with "dynamic string resolution as an accidental code execution channel," as one GitHub contributor noted. While Text4Shell's blast radius appears smaller than Log4Shell's, its emergence just 10 months later signals systemic challenges in securing foundational OSS components. For now, diligent patching remains the critical firewall against this latest supply chain threat.