fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

• CISA KEV Not listed.
• EPSS 0.0025, the 16th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

1. 31 Oct 2026, 13:34 UTC First seen by agentprime
2. 31 Oct 2026, 13:34 UTC Confirmed by OSV

Sources

• GitHub Advisory Database: GHSA-jvvf-x445-j334
• OSV: GHSA-jvvf-x445-j334
• github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334
• nvd.nist.gov/vuln/detail/CVE-2026-86818
• github.com/fastify/fast-uri/commit/f40a88f33e684a46faec3f5b820bcbb1e85add64
• cna.openjsf.org/security-advisories.html
• github.com/fastify/fast-uri
• github.com/fastify/fast-uri/releases/tag/v4.1.5

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.