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CVE-2026-45721

Improper Input Validation: Is CVE-2026-45721 real, exploitable, or a false positive? Here's the community verdict.

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signals

public sources

Exploited in wild
Not listed
CISA KEV
Public exploit
None known
Metasploit/EDB/PoC
Base severity
9 Critical
CVSS
Exploitation prob.
0.4%
FIRST EPSS
Weakness
CWE-20 · Improper Input Validation
CWE

High CVSS base score, but low real-world exploitation probability (EPSS). Likely less urgent than the score implies.

baseline read

auto · not a community verdict

Real, but low real-world risk

A genuine vulnerability on paper, but EPSS shows little real-world exploitation — the base score may overstate urgency. This is not the same as a false positive.

Based on CVSS · FIRST EPSS

Confirm or dispute →

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, when Algernon is asked for any URL path that resolves to a directory without an index file, DirPage walks upward through parent directories — past the configured server root — looking for a file named handler.lua to execute as the request handler. The loop terminates only after 100 ancestor steps or when filepath.Dir returns ., so on any absolute server-root path the search reaches the filesystem root (/ on Unix, drive letter on Windows). The first handler.lua it finds is loaded into the Lua interpreter with the full Algernon API exposed — including run3(), httpclient, os.execute, io.popen, PQ, MSSQL, raw filesystem access, and the userstate database. Any process that can write handler.lua anywhere in a parent directory of the server root obtains pre-authenticated remote code execution on the next HTTP request. This is reachable without authentication — the lookup happens before the permission check returns a hit (the perm system only gates URL prefixes, not the handler-resolution step), and any URL pointing at a directory without an index triggers the walk. On a fresh stock Algernon install the request GET / is enough. This vulnerability is fixed in 1.17.7.

References

NVD MITRE CVE.org

Published

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In your experience, is this finding real and exploitable?

awaiting field verdicts
Real, but not a risk here
Not a real issue

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Field notes & remediation

Verdicts are the quick signal. Notes are the evidence and fixes behind them.

  • 0
    Field note · TruePositive EditorialCurated

    This scores high on paper (CVSS 9) but the real-world signal is low. It is not in CISA KEV and no public exploit was found, and near-term exploitation looks unlikely (EPSS about 0%). Verify your own exposure before treating it as urgent. It is reachable over the network with no authentication and no user interaction, which is the most dangerous profile. Not an emergency for most teams, but patch it in your normal cycle and check whether the affected component is actually exposed in your setup.

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Related CVEs

Same weakness: CWE-20 · Improper Input Validation.