CVE-2021-29456

MEDIUMNVD 5.75.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.7 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 60% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this week
5.7
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 1%CVSS: 5.7Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Authelia is an open-source authentication and authorization server providing 2-factor authentication and single sign-on (SSO) for your applications via a web portal. In versions 4.27.4 and earlier, utilizing a HTTP query parameter an attacker is able to redirect users from the web application to any domain, including potentially malicious sites. This security issue does not directly impact the security of the web application itself. As a workaround, one can use a reverse proxy to strip the query parameter from the affected endpoint. There is a patch for version 4.28.0.

CVSS v3
5.7
EG Score
5.7(medium)
EG Risk
30(Track)
EG Risk 30/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity57% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
40.4%
KEV
Not listed

Published

April 21, 2021

Last Modified

November 21, 2024

References (2)

Affected Packages

(1 across 1 ecosystem)
Go(1)
PackageVulnerable rangeFixed inDependents
github.com/authelia/authelia/v4—4.28.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 15× in last 7d / 52× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 102 total refreshes for this CVE.

  1. 2026-07-23 14:16 UTCEPSS rescore
  2. 2026-07-23 01:59 UTCEG score recompute
  3. 2026-07-22 22:46 UTCEG score recompute
  4. 2026-07-22 14:06 UTCEPSS rescore
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  1. 2026-07-09 19:07 UTCEPSS rescore
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  44. 2026-06-13 08:43 UTCOSV refresh
  45. 2026-06-12 23:10 UTCEPSS rescore
  46. 2026-06-11 13:58 UTCEPSS rescore
  47. 2026-06-10 22:16 UTCEPSS rescore
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  74. 2026-05-26 18:01 UTCEG score recompute
  75. 2026-05-26 13:42 UTCEPSS rescore

Frequently asked(5)

What is CVE-2021-29456?
CVE-2021-29456 is a medium vulnerability published on April 21, 2021. Authelia is an open-source authentication and authorization server providing 2-factor authentication and single sign-on (SSO) for your applications via a web portal. In versions 4.27.4 and earlier, utilizing a HTTP query parameter an attacker is able to redirect users from the web application to…
When was CVE-2021-29456 disclosed?
CVE-2021-29456 was first published in the National Vulnerability Database on April 21, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-29456 actively exploited?
CVE-2021-29456 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 40.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-29456?
CVE-2021-29456 has a CVSS v3 base score of 5.7 (NVD).
How do I remediate CVE-2021-29456?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-29456, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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