CVE-2026-54739
MEDIUMDescription
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 to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v4 Vector
Exploitability
Impact
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Exploit Intelligence
Low risk: more likely to be exploited than 36% of all known CVEs.
References
Related Vulnerabilities
Other CWE-204 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-41697 | Medium | 5.3 | 20% | - | - |
| CVE-2016-9499 | Medium | 5.3 | 7.8% | - | Fix |
| CVE-2019-19030 | Medium | 5.3 | 1.9% | - | Fix |
| CVE-2022-0564 | Medium | 5.3 | 1.4% | - | Fix |
| CVE-2021-20049 | High | 7.5 | 1.3% | - | Fix |
| CVE-2021-39189 | Medium | 5.3 | 1.3% | - | Fix |
Common questions
How do I fix CVE-2026-54739?
No published fix for CVE-2026-54739 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-54739 being actively exploited?
Not that we know of. CVE-2026-54739 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.43% is the estimated probability that it will be exploited in the next 30 days. That is higher than 36% of all scored CVEs.
How severe is CVE-2026-54739?
CVE-2026-54739 has a CVSS v4 base score of 6.9, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
Embed a live status badge for CVE-2026-54739
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-21.