LemmyNet Lemmy up to 0.19.18/1.0.0-beta.0 Rate Limiting mod.rs realip_remote_addr X-Forwarded-For improper authentication

Summaryinfo

A vulnerability, which was classified as critical, has been found in LemmyNet Lemmy up to 0.19.18/1.0.0-beta.0. The affected element is the function ConnectionInfo::realip_remote_addr of the file crates/utils/src/rate_limit/mod.rs of the component Rate Limiting. The manipulation of the argument X-Forwarded-For leads to improper authentication. This vulnerability is listed as CVE-2026-54738. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in LemmyNet Lemmy up to 0.19.18/1.0.0-beta.0. It has been rated as critical. This issue affects the function ConnectionInfo::realip_remote_addr of the file crates/utils/src/rate_limit/mod.rs of the component Rate Limiting. The manipulation of the argument X-Forwarded-For with an unknown input leads to a improper authentication vulnerability. Using CWE to declare the problem leads to CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Impacted is integrity, and availability. The summary by CVE is:

Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, actix-web ConnectionInfo::realip_remote_addr reads the first value of X-Forwarded-For as the client address used by raw_ip_key in crates/utils/src/rate_limit/mod.rs. Lemmy's bundled docker/nginx.conf uses $proxy_add_x_forwarded_for instead of $remote_addr, which appends the real client address to an X-Forwarded-For value supplied by the client. An unauthenticated attacker can therefore place a different spoofed address first on each request and receive a new rate-limit bucket, bypassing limits on POST /api/v4/account/auth/register, POST /api/v4/account/auth/login, POST /api/v4/post, POST /api/v4/comment, GET /api/v4/search, POST /api/v4/image, and POST /api/v4/account/import_settings. This permits excessive account creation, brute-force attempts, spam, scraping, uploads, and repeated imports. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-54738 since 06/16/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 0.19.19 or 1.0.0-beta.1 eliminates this vulnerability.

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Productinfo

Vendor

• LemmyNet

Name

• Lemmy

Version

• 0.19.0
• 0.19.1
• 0.19.2
• 0.19.3
• 0.19.4
• 0.19.5
• 0.19.6
• 0.19.7
• 0.19.8
• 0.19.9
• 0.19.10
• 0.19.11
• 0.19.12
• 0.19.13
• 0.19.14
• 0.19.15
• 0.19.16
• 0.19.17
• 0.19.18
• 1.0.0-beta

Website

• Product: https://github.com/LemmyNet/lemmy/

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