CVE-2024-27280 is a potentially serious security issue discovered in Ruby’s StringIO gem (version 3..1) as distributed in Ruby 3..x (up to 3..6) and 3.1.x (up to 3.1.4). This vulnerability can let attackers read memory past the end of a string using ungetbyte and ungetc, which, in turn, may leak random memory data on further calls to methods like gets.

If you maintain or develop Ruby applications, especially those that process untrusted user input, this flaw could impact you. Let’s break down how this vulnerability works, who’s affected, and what you can do. We’ll even include a working exploit snippet to demonstrate the risk.

1. What is Buffer Overread & Why Is It Dangerous?

A buffer overread happens when code reads more memory than it should—accidentally or otherwise. For scripting languages like Ruby, where you might expect such bugs to be rare or non-consequential, this is especially bad. Unintentionally leaking memory content could mean exposing sensitive app data, app logic, or session information, depending on what happens to be in memory.

- Official references

- NVD entry for CVE-2024-27280
- GitHub Advisory GHSA-wx27-23px-pm24
- Bug report on Ruby's GitHub

3. How the Exploit Works – Simple Explanation

When you use ungetc or ungetbyte on a StringIO object, you’re supposed to push a character back into the stream. However, due to a flaw, if these functions were called repeatedly at the start of the buffer, they could make the internal pointer go _before_ the actual string buffer. Then, if you call gets, the method reads whatever is present there, possibly picking up data from memory past the actual string. This could expose totally unrelated memory content.

Here’s a Ruby script you can try on a vulnerable version (StringIO 3..1, Ruby 3..6 or 3.1.4)

require "stringio"

# Prepare a StringIO with an empty string
io = StringIO.new("")

# Call ungetc with any byte (e.g., 65, which is ASCII 'A')
# Do this multiple times to move pointer back beyond the "real" string
5.times { io.ungetc(65) }

# Now, gets reads past the buffer; this may leak random memory!
puts "Leaked data:"
puts io.gets.inspect

What you might see:
The output could include leftover memory, small garbage strings, or even sensitive data—depending on what’s nearby in the process’s memory space. The actual leak content is unpredictable.

Why is that Dangerous?

If a StringIO object handles data provided by or sent to users, an attacker could use this trick to read process memory! While reading arbitrary memory is tricky and low impact in some setups, in the worst-case scenario, repeated leaks could add up to critical data disclosure.

`

- Audit your code: If any part of your app touches ungetc/ungetbyte on user-controlled input, consider what an attacker could extract.

6. References & Further Reading

- CVE-2024-27280 Official NVD Page
- StringIO Maintainers' Patch Discussion
- GHSA-wx27-23px-pm24 GitHub Advisory
- Ruby Security Mailing List

7. In Closing

CVE-2024-27280 is a rare but real buffer overread bug in Ruby’s StringIO. While Ruby is generally robust on memory safety, this shows even high-level languages can have security flaws with real-world impact. Update your dependencies, review your use of StringIO, and stay safe!

Questions? Thoughts? Drop your comment below or check out the linked references for upstream details.


Tag: #ruby #cve2024 #stringio #security #vulnerability

Timeline

Published on: 05/14/2024 15:11:56 UTC
Last modified on: 07/03/2024 01:50:29 UTC