MessagePack::Buffer#clear Use-After-Free that Enables Cross-Buffer Disclosure

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 0.0023, the 13th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

1. 31 Oct 2026, 15:16 UTC First seen by agentprime
2. 31 Oct 2026, 15:16 UTC Confirmed by OSV

Sources

• GitHub Advisory Database: GHSA-4mrv-5p47-p938
• OSV: GHSA-4mrv-5p47-p938
• github.com/msgpack/msgpack-ruby/security/advisories/GHSA-4mrv-5p47-p938
• github.com/msgpack/msgpack-ruby/commit/5627d71606b565641d2dd501b82aae862f4abe90
• github.com/msgpack/msgpack-ruby
• github.com/rubysec/ruby-advisory-db/blob/master/gems/msgpack/CVE-2026-54522.yml
• www.cve.org/CVERecord/SearchResults?query=CVE-2026-54522

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.