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  4. CVE 2026 104421 zebra before 621 block download denial of service
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Back to active CVEs
Medium · CVSS 6.9CVE-2026-104421

Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockout

Answer in brief

CVE-2026-104421 records a Medium severity (CVSS 6.9) vulnerability in Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockout. The current sources do not mark it as known exploited. The current feed maps ZcashFoundation/zebra (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 2, 2026Updated Oct 2, 2026Source checked Oct 2, 2026First seen by HOL Oct 2, 2026Material review Oct 2, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 6.9
Exploitation
Not marked as known exploited
Affected software
1 mapped package or product
Fix availability
Available

Why this deserves its current priority

CVSS is 6.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps ZcashFoundation/zebra (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
ZcashFoundation/zebrageneric>=0 <6.2.16.2.1

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for ZcashFoundation/zebra.
  2. 2Review the reported fix. Update ZcashFoundation/zebra to 6.2.1 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Oct 2, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Oct 2, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Oct 2, 2026

Sources and claim methodology

  • GitHub security advisorygithub.com
  • Source referencevulncheck.com
Upstream source 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.

Quoted source text, attributed separately from HOL analysis.

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Record context

Vulnerability class
Missing Auth
EPSS
Not reported
CWE IDs
CWE-459
Source
CVE List V5
Source checked
Oct 2, 2026
References
2 linked sources
Open source record