Vulnerability · Published Oct 2, 2026 · Assigned by VulnCheck
CVE-2026-104421Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockout
Medium 5.3
In plain English
A medium-severity security flaw in zebra from ZcashFoundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities).
Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.3%top 76.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
Zebra before 6.2.1 contains an incomplete cleanup vulnerability that allows unauthenticated peers to block downloading of valid blocks by leaving rejected hashes in SentHashes. Attackers can send a contextually invalid block sharing an honest block's header hash, causing Request::KnownBlock to skip the honest block and keep nodes behind the tip.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| ZcashFoundation | zebra | 0 – before 6.2.1 |
Weakness: CWE-459 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L