CVE-2026-45728 Algernon: Single-file mode unconditionally enables debug mode
Attackers can read server-side source code and data files by triggering errors in single-file mode, which inadvertently enables debug mode.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45728?
CVE-2026-45728 is a high-severity vulnerability in xyproto algernon, published on 26 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, when Algernon is invoked with a single file path instead of a directory, singleFileMode is set to true and debugMode is forcibly enabled. debugMode activates the PrettyError renderer, which on any Lua or template error response dumps the absolute path of the file that errored, complete byte contents of that file, and exception or parser error text. This response is served with HTTP 200 OK to whoever sent the request that triggered the error. Any client able to reach the server and able to provoke a runtime error in the served script obtains the full server-side source of that script and of any sibling Lua data file consulted during the request. This vulnerability is fixed in 1.17.7.
Which versions are affected by CVE-2026-45728?
3 open source packages ship an affected version, including github.com/xyproto/algernon.
| Package | Affected | Fixed in |
|---|---|---|
github.com/xyproto/algernon Go | All versions | 1.17.7 |
github.com/xyproto/algernon Go | All versions | 1.17.7 |
github.com/xyproto/algernon Go | All versions | 1.17.7 |
How do I fix CVE-2026-45728?
Upgrade github.com/xyproto/algernon to 1.17.7 or later.
Is CVE-2026-45728 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45728 exists.
Sources
Also known as GHSA-fwqx-8365-9983, GO-2026-5385.