CVE-2021-41054

What it actually does

The flaw triggers a buffer overflow in tftpd_file.c when the daemon processes combined data, OACK, and option packets without correctly sizing the receive buffer, resulting in memory corruption that crashes the process.

Why it matters to the business

TFTP-based services such as network boot, firmware distribution, or configuration file transfers become unavailable, causing operational outages for dependent systems.

How an attack unfolds

An attacker sends a single crafted TFTP request containing a specific combination of data and option fields that exceed the expected buffer size, causing the atftp daemon to overflow and terminate.

How to fix it

Upgrade atftp to the latest maintained release that corrects buffer handling in tftpd_file.c; where packages remain at 0.7.4 or earlier, replace the daemon with a maintained alternative or apply vendor patches if supplied.

How to confirm the fix worked

Confirm the installed atftp version is newer than 0.7.4, then replay a minimal test packet set that previously triggered the overflow and verify the daemon remains stable.

Typical attack path

1. Locate publicly reachable atftp servers
2. Craft a TFTP RRQ or WRQ packet embedding oversized option combinations
3. Transmit the packet to trigger the overflow
4. Observe daemon crash and service denial

How to detect it

Review TFTP daemon logs and system crash reports for abrupt atftpd terminations correlated with inbound TFTP traffic from untrusted sources.

What your security team should do

• Inventory all systems running atftp and schedule immediate upgrades
• Restrict TFTP access to trusted subnets via firewall rules
• Monitor process and system logs for unexpected atftpd terminations
• Replace atftp with a supported TFTP implementation where upgrades are unavailable