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fix(challenge/metarefresh): ensure that clients have waited long enough #1068

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merged 1 commit into from
Aug 31, 2025
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fix(challenge/metarefresh): ensure that clients have waited long enough #1068

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3 changes: 2 additions & 1 deletion docs/docs/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

- Add a "proof of React" challenge to prove that the client is able to run a simple JSX app.
- Added possibility to disable HTTP keep-alive to support backends not properly
handling it
handling it.
- Add a server-side check for the meta-refresh challenge that makes sure clients have waited for at least 95% of the time that they should.
- Added a missing link to the Caddy installation environment in the installation documentation.
- Downstream consumers can change the default [log/slog#Logger](https://pkg.go.dev/log/slog#Logger) instance that Anubis uses by setting `opts.Logger` to your slog instance of choice ([#864](https://github.com/TecharoHQ/anubis/issues/864)).
- The [Thoth client](https://anubis.techaro.lol/docs/admin/thoth) is now public in the repo instead of being an internal package.
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7 changes: 7 additions & 0 deletions lib/challenge/metarefresh/metarefresh.go
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Expand Up @@ -5,6 +5,7 @@ import (
"fmt"
"log/slog"
"net/http"
"time"

"github.com/TecharoHQ/anubis"
"github.com/TecharoHQ/anubis/lib/challenge"
Expand Down Expand Up @@ -42,6 +43,12 @@ func (i *Impl) Issue(r *http.Request, lg *slog.Logger, in *challenge.IssueInput)
}

func (i *Impl) Validate(r *http.Request, lg *slog.Logger, in *challenge.ValidateInput) error {
wantTime := in.Challenge.IssuedAt.Add(time.Duration(in.Rule.Challenge.Difficulty) * 950 * time.Millisecond)

if time.Now().Before(wantTime) {
return challenge.NewError("validate", "insufficent time", fmt.Errorf("%w: wanted user to wait until at least %s", challenge.ErrFailed, wantTime.Format(time.RFC3339)))
}

gotChallenge := r.FormValue("challenge")

if subtle.ConstantTimeCompare([]byte(in.Challenge.RandomData), []byte(gotChallenge)) != 1 {
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