CVE-2025-33042: Schema to Shell: Unpacking the Apache Avro Code Injection Vulnerability

Source: Dev.to

Overview

Apache Avro, the serialization backbone of the big‑data ecosystem, contained a critical code‑injection vulnerability in its Java SDK. The flaw allowed attackers to weaponize Avro schemas—normally benign JSON definitions—to inject arbitrary Java code during the compilation phase. By manipulating metadata fields such as documentation or annotations, a malicious schema could trick the SpecificCompiler into generating a Trojan‑horse Java class. This turns a standard build process into a Remote Code Execution (RCE) vector, threatening developer workstations and CI/CD pipelines alike.

TL;DR

The Apache Avro Java SDK failed to sanitize schema metadata before generating Java source code. An attacker can craft a malicious schema that, when compiled by a developer or build server, injects and executes arbitrary Java code (RCE). Fixed in versions 1.11.5 and 1.12.1.

Exploit Status

POC (Proof‑of‑Concept)

Technical Details

• Vulnerability ID: CVE-2025-33042
• CVSS Score: 7.3 (High)
• CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• CWE: CWE‑94 (Code Injection)
• Impact: Remote Code Execution (build‑time or run‑time)
• Fix Versions: 1.11.5, 1.12.1

Affected Systems

• Apache Avro Java SDK version 1.12.0 (fixed in 1.12.1)
• Earlier vulnerable releases include 1.11.x prior to 1.11.5.

Code Analysis

Commit: 84bc732 – AVRO‑4053: [Java] Validate specific compiler output

@@ -95,6 +95,8 @@
+    public static String escapeForJavadoc(String doc) {
+        if (doc == null) return null;
+        return doc.replace("*/", "*/");
+    }

The change introduces escapeForJavadoc, which sanitizes the */ sequence that could otherwise break out of Javadoc comments and allow static‑initializer injection.

Exploit Details

A hypothetical exploit demonstrates a Javadoc breakout via the */ sequence, enabling an attacker to inject malicious static initializers into the generated Java class.

Mitigation Strategies

• Input Validation: Sanitize all schema metadata before compilation.
• Output Encoding: Escape characters that could terminate comment blocks or strings.
• Dependency Management: Keep Avro libraries up‑to‑date.
• Build Isolation: Run builds in ephemeral containers with minimal privileges.

Remediation Steps

1. Update org.apache.avro:avro and org.apache.avro:avro-compiler to 1.11.5 or 1.12.1 immediately.
2. If using avro-maven-plugin or avro-gradle-plugin, upgrade the plugin to a version that bundles the patched SDK.
3. Audit your codebase for Avro schemas (.avsc or .avpr) that have been modified by untrusted contributors.
4. As a defense‑in‑depth measure, execute build pipelines in isolated containers without access to sensitive secrets unless strictly necessary.

References

• Apache Avro Mailing List Announcement
• JIRA Issue AVRO‑4053
• OSS‑Security Advisory (2026‑02‑12)
• Full CVE‑2025‑33042 Report