A newly disclosed vulnerability in the Apache Commons Text library has triggered alarms across the Java ecosystem, evoking memories of the widespread Log4Shell crisis. Designated CVE-2022-42889 and colloquially dubbed "Text4Shell," this critical flaw (CVSS 9.8) enables remote code execution through the library's string interpolation feature.

Vulnerability Mechanics

The flaw resides in the StringSubstitutor class, which processes placeholders in text. When using the default interpolator (StringSubstitutor.createInterpolator()), attackers can exploit the script, dns, or url lookup capabilities to execute arbitrary code via crafted input:

String payload = "${script:javascript:java.lang.Runtime.getRuntime().exec('calc.exe')}";
StringSubstitutor.replace(payload, StringSubstitutor.createInterpolator());

Critical Differences from Log4Shell

While reminiscent of Log4Shell, key distinctions exist:
- Lower Ubiquity: Commons Text lacks Log4j's near-universal adoption
- Explicit Enablement: Exploitation requires explicit use of interpolation features
- Mitigation Complexity: Unlike Log4j's ubiquitous logging, affected Commons Text use cases vary widely

Attack Vectors

Exploitable scenarios include:
1. Web applications processing user-controlled strings with interpolation
2. Configuration files parsing attacker-supplied values
3. Data transformation pipelines accepting external inputs

Mitigation Steps

Apache released version 1.10 disabling dangerous interpolators by default. Developers must:
1. Immediately upgrade dependencies to commons-text 1.10+
2. Audit code for StringSubstitutor usage with interpolation enabled
3. If unable to patch, disable interpolators via -Dorg.apache.commons.text.StringSubstitutor.disableInterpolatorSystems=true

"This isn't another Log4j, but it's a stark reminder that string parsing libraries remain potent attack surfaces," noted security researcher @ricci, who highlighted the vulnerability. "Defense-in-depth demands scrutinizing all dependencies—not just the obvious ones."

The Text4Shell disclosure underscores persistent risks in foundational open-source components. As the industry continues grappling with supply chain security, this incident reinforces that even narrowly-scoped libraries can harbor critical flaws when their capabilities intersect with untrusted data. Vigilant patching and input validation remain non-negotiable defenses.

Source: Mastodon Technical Discussion (@ricci)