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Vulnerabilities

Vulnerability · CVE-2026-46431

Algernon is a small self-contained pure-Go web server.

Published May 26, 2026 · catalog updated Jul 24, 2026 · Algernon is a small

Check if you run it

No confirmed exploitation is on record for CVE-2026-46431. EPSS is 0.31%. Act only if a listed version of Algernon is a small is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Algernon is a small).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium4.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.31%
Remediation
Advisory link
Affected products
See sources for product scope

Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server's Access-Control-Allow-Origin response header was hardcoded to the wildcard * regardless of the caller's Origin. Because EventSource does not preflight and does not send cookies, the wildcard is sufficient to let any third-party page the developer visits open a cross-origin EventSource to the SSE port and read the live filename stream from JavaScript. This vulnerability is fixed in 1.17.7.

No affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.

How to fix CVE-2026-46431

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-46431. EPSS is 0.31%. Act only if a listed version of Algernon is a small is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-942: Permissive Cross-domain Policy with Untrusted Domains. EPSS 0.31%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. May 26, 2026 · NIST NVD

    Detected

    Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server's Access-Control-Allow-Origin response header was hardcoded to the wildcard * regardless of the caller's Origin. Because EventSource does not preflight and does not send cookies, the wildcard is sufficient to let any third-party page the developer visits open a cross-origin EventSource to the SSE port and

  2. Jul 24, 2026 · NIST NVD

    Updated

    Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server's Access-Control-Allow-Origin response header was hardcoded to the wildcard * regardless of the caller's Origin. Because EventSource does not preflight and does not send cookies, the wildcard is sufficient to let any third-party page the developer visits open a cross-origin EventSource to the SSE port and

Sources

  • CVE.orgVulnerability recordCVE-2026-46431

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-46431

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-2026-46431

    Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, the SSE event server's Access-Control-Allow-Origin response header was hardcoded to the wildcard * regardless of the caller's Origin. Because EventSource does not preflight and does not send cookies, the wild

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.