vulnerability / NVI-00017564 / Revision 1
Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir
GitHub lists this reviewed advisory for github.com/xyproto/algernon. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
8.2 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
github.com/xyproto/algernon
source listed<= 1.17.7
### Summary When algernon is started with `--domain` (or `--letsencrypt`, which silently turns on `--domain` at `engine/flags.go:372`), the request handler resolves the served directory by joining the configured `--dir` with the value of the client-supplied `Host` header. The join is performed by `filepath.Join` with no validation, so a `Host: ..` header walks one level above the document root. Subsequent file resolution then exposes everything in that parent directory — arbitrary file read, full directory listing, and, if any `.lua` file is present, server-side Lua execution. Algernon 1.17.7 and earlier are affected. ### Details `engine/handlers.go` (function `RegisterHandlers`, around line 510): ```go allRequests := func(w http.ResponseWriter, req *http.Request) { ... servedir := servedir if addDomain { servedir = filepath.Join(servedir, utils.GetDomain(req)) // <— line 531 } ... filename := utils.URL2filename(servedir, urlpath) ``` `utils/web.go` (`GetDomain`): ```go func GetDomain(req *http.Request) string { host, _, err := net.SplitHostPort(req.Host) if err != nil { return req.Host // <— Host header returned verb
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-jc3j-x6pg-4hmv ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.