On March 6, 2024, a significant vulnerability was disclosed for the uAMQP C library, which is widely used to enable communication with Azure Cloud Services via the AMQP 1. protocol. Tracked as CVE-2024-27099, this flaw exists in how the library processes incorrect or failed AMQP_VALUE states, potentially leading to a *double free* issue. The exploit can precipitously lead to remote code execution (RCE) on servers or applications utilizing vulnerable versions of uAMQP.

This article breaks down the vulnerability in plain language, shows you code excerpts, links the original sources, explains what a double free is, demonstrates an example exploit, and finally, gives solutions to safeguard your systems.

What is uAMQP?

uAMQP is an open-source C library developed by Microsoft for handling AMQP 1. protocol communication — it's integral for IoT devices, messaging solutions, and services interacting with Azure Cloud. Its small footprint and efficiency make it highly popular for embedded and server use.

The Core Problem

In certain code paths, uAMQP failed to correctly handle errors arising from invalid AMQP_VALUE states. When cleanup routines were called after a failure, the same memory pointer could accidentally be freed twice — a classic "double free" bug.

A double free happens when the same chunk of memory is returned to the system more than once. Attackers can exploit such bugs to corrupt memory allocation tables, alter program flow, or inject malicious code — all of which could lead to Remote Code Execution (RCE).

Here’s a simplified code snippet inspired by the core issue

AMQP_VALUE value = amqpvalue_create_int(42);
// ... some code ...

if (handle_incorrect_value(value) != ) {
    amqpvalue_destroy(value);
    // Error state: value pointer still points to same memory
    // but may get double-freed below
}

amqpvalue_destroy(value); // Double free happens here!

When error handling is triggered (e.g., invalid state), the pointer is freed once in the error block, then again in the normal cleanup code — leading to undefined and dangerous behavior.

Critical Paths

- The bug primarily affects code paths or applications that process untrusted or malformed AMQP payloads using the vulnerable version of uAMQP.
- Application code that doesn't manage the return values carefully and cleans up objects twice is likely at risk.

Exploitability: From Bug to RCE

If an attacker can control or craft malformed AMQP data processed by the vulnerable server/client, they can reliably trigger the double free. In real-world scenarios, this can result in arbitrary code execution with the privileges of the affected process.

Code execution achieved — attacker gains control over the system.

Note: The above is a conceptual attack path. On Linux/x86-64, double free bugs are exploitable depending on several heap conditions and security mitigations active on the system (ASLR, heap hardening, etc.).

Official Patch & Fix

The uAMQP team has patched the double free in commit 2ca42b6e4e098af2d17e487814a91d05f6ae4987.

If you're using uAMQP as a submodule or direct source, update as follows

git submodule update --remote --merge --init
cd azure-uamqp-c
git checkout 2ca42b6e4e098af2d17e487814a91d05f6ae4987

More Information and References

- Original Advisory: GitHub Security Advisory for uAMQP *(placeholder — check the repo’s security tab)*
- Official Patch Commit: Azure/azure-uamqp-c@2ca42b6
- Public CVE Record: CVE-2024-27099 at NVD
- uAMQP Documentation: Microsoft Docs

Monitor: Watch for suspicious AMQP connections or errors in your application logs.

- Stay Updated: Subscribe to the uAMQP repo and security mailing lists.

Double free bugs, especially in networking libraries, have a long history of being a stepping stone for critical attacks. Don’t take this lightly — patch now to keep your Azure-connected applications safe.


*Exclusive write-up by ChatGPT. Please link back if you share.*

Timeline

Published on: 02/27/2024 19:04:07 UTC
Last modified on: 02/28/2024 14:06:45 UTC