CVE-2025-54799: Let's Encrypt client and ACME library written in Go (Lego).

Let's Encrypt client and ACME library written in Go (Lego).

Let's Encrypt client and ACME library written in Go (Lego). In versions 4.25.1 and below, the github.com/go-acme/lego/v4/acme/api package (thus the lego library and the lego cli as well) don't enforce HTTPS when talking to CAs as an ACME client. Unlike the http-01 challenge which solves an ACME challenge over unencrypted HTTP, the ACME protocol requires HTTPS when a client communicates with the CA to performs ACME functions. However, the library fails to enforce HTTPS both in the original discover URL (configured by the library user) and in the subsequent addresses returned by the CAs in the directory and order objects. If users input HTTP URLs or CAs misconfigure endpoints, protocol operations occur over HTTP instead of HTTPS. This compromises privacy by exposing request/response details like account and request identifiers to network attackers. This was fixed in version 4.25.2.

Description from the National Vulnerability Database, published by GitHub

What it means for a small business

If your business uses lego, install the vendor's update. If you're not sure whether you use it, ask whoever manages your computers.

How likely is an attack? The Exploit Prediction Scoring System, run by FIRST (the global association of security response teams), puts the odds of this one being exploited in the next 30 days at 0.24%, higher than 14% of CVEs. That’s low, but low isn’t zero, and the odds jump the day someone publishes an exploit. Scored October 29, 2026, updated daily.

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Sources

Part of the Huttenlocher Technologies vulnerability database, refreshed twice a day from CISA and the NVD. The title, category and plain-language guidance are ours; check the linked record before acting on a detail. This is general guidance, not a review of your systems.

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