algernon: Improper Handling of Windows ::DATA Alternate Data Stream
CVE-2026-52792 is a high-severity improper handling of windows ::DATA alternate data stream vulnerability in algernon from Xyproto, with a CVSS 4.0 base score of 8.7 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected algernon versions: < 1.17.9. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.63% chance of exploitation within 30 days, higher than 51% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of algernon you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Attack requirements
- NoneThe attack does not depend on a particular deployment or configuration.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Confidentiality (vulnerable system)
- HighSerious loss of confidentiality on the vulnerable system.
- Integrity (vulnerable system)
- NoneNo loss of integrity on the vulnerable system.
- Availability (vulnerable system)
- NoneNo loss of availability on the vulnerable system.
- Confidentiality (other systems)
- NoneNo loss of confidentiality on systems beyond the vulnerable one.
- Integrity (other systems)
- NoneNo loss of integrity on systems beyond the vulnerable one.
- Availability (other systems)
- NoneNo loss of availability on systems beyond the vulnerable one.
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (github.com).
Official description
Algernon is a small self-contained pure-Go web server. Prior to 1.17.9, Algernon on Windows selects a file handler in engine/handlers.go by calling filepath.Ext() without first rejecting NTFS-equivalent names such as x.lua::$DATA, x.lua., and x.lua . An unauthenticated client can append one of these suffixes to a public server-side script using the .lua, .tl, .po2, .amber, or .frm extension. The request path passes through URL2filename in utils/files.go, skips the renderer and execution cases, and reaches FilePage, os.Open, ReadAndLogErrors, and ToClient, while NTFS resolves the alias to the underlying script. The server consequently returns raw script source and can expose database credentials, API keys, and the SetCookieSecret value, which may permit forged session cookies. Linux and macOS hosts are not affected by this issue. This issue is fixed in version 1.17.9.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Handling of Windows ::DATA Alternate Data Stream
The product does not properly prevent access to, or detect usage of, alternate data streams (ADS).
How developers prevent this class of flaw
- Ensure that the source code correctly parses the filename to read or write to the correct stream.
More Improper Handling of Windows ::DATA Alternate Data Stream vulnerabilities (CWE-69)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in algernon
- 9.4 Critical severity
- 8.2 High severity
- 7.5 High severity
- 9.0 Critical severity
- 8.7 High severity
- 8.2 High severity
Recent Improper Handling of Windows ::DATA Alternate Data Stream vulnerabilities
- 8.8 High severity
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