CVE-2026-45728
HIGHCVE-2026-45728 is a high-severity (CVSS 7.5) CWE-209 vulnerability in github.com/xyproto/algernon. O3 Security confirms whether CVE-2026-45728 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Algernon: Single-file mode unconditionally enables debug mode
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-45728.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-45728 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/xyproto/algernonReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/xyproto/algernon | all versions | 1.17.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/xyproto/algernon. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/xyproto/algernon to 1.17.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45728 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-45728 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-45728. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-45728 in your dependencies?
O3 detects CVE-2026-45728 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.