CVE-2026-54739

Description

Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, Lemmy's login endpoint in crates/api/api/src/local_user/login.rs returns different errors depending on whether the username_or_email value exists. LocalUserView::find_by_email_or_name propagates a NotFound response for an unknown account, while an existing account with a wrong password returns LemmyErrorType::IncorrectLogin. This observable response discrepancy, including HTTP 404 for a nonexistent account and HTTP 400 for an incorrect password on an existing account, allows an unauthenticated attacker to confirm registered usernames or email addresses and use the results for targeted credential attacks or social engineering. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.

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EPSS — Exploit Prediction

0.0043

Probability of exploitation

0.36%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-204 CWE-204

References

Other References

https://github.com/LemmyNet/lemmy/commit/4d235a1b668b7dda6b73dbbc9ca289bb40acfa83 https://github.com/LemmyNet/lemmy/commit/59e968a5ac36d36d08a59028e2dbb92641536964 https://github.com/LemmyNet/lemmy/pull/6531 https://github.com/LemmyNet/lemmy/pull/6535 https://github.com/LemmyNet/lemmy/releases/tag/0.19.19 https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-beta.1 https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xgg7-8hvq-8m65 https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19

Frequently Asked Questions

What is CVE-2026-54739? +

Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, Lemmy's login endpoint in crates/api/api/src/local_user/login.rs returns different errors depending on whether the username_or_email value exists. LocalUserView::find_by_email_or_name propagates a NotFound response for an unknown account, while an existing account with a wrong password returns LemmyErrorType::IncorrectLogin. This observable response discrepancy, including HTTP 404 for a nonexistent account and HTTP 400 for an incorrect password on an existing account, allows an unauthenticated attacker to confirm registered usernames or email addresses and use the results for targeted credential attacks or social engineering. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.

How do I check if I'm vulnerable to CVE-2026-54739? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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