Zebra: Denial of service via quadratic complexity in block transparent value check
Summary
Zebra, the Rust full-node implementation of the Zcash network, has an algorithmic complexity flaw in block validation. For each transaction, the check copies the block-wide spent-output map, so validation time grows quadratically with the number of transactions. An attacker who mines a block, or seeds the public mempool so that an honest miner includes such transactions, can stall every validating node for over 52 seconds; the trigger requires a valid proof-of-work block, and no crash, consensus divergence or data corruption is reported.
Affected
- Zebra (zebrad) versions before 6.1.0 according to the CNA range (affected 0 to less than 6.1.0)
- One secondary source lists only 6.0.0 as affected; this could not be confirmed, so all versions below 6.1.0 should be treated as affected
Fixed in
- Zebra 6.1.0 (fix PR #10995, advisory GHSA-4g24-549m-hp75)
Workaround
- No configuration-only workaround is documented. Patching is the only known remedy.
Exploitation
- CISA SSVC: exploitation none, automatable no, technical impact partial.
- Not listed in CISA KEV according to a third-party tracker.
- No public proof of concept or exploitation reports found.
Our recommendation
- If you operate a Zebra node, upgrade to 6.1.0 or the current release line.
- Check whether Zcash node software is present in your environment, for example at exchanges, custodians, wallet backends or mining operations.
- Monitor node performance and block validation times for unusual stalls.
- Organisations without Zebra nodes need no action for this CVE.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-4g24-549m-hp75 github.com
- VulnCheck advisory www.vulncheck.com
- Zebra 6.1.0 release github.com
- Zcash Foundation Zebra 6.1.0 post zfnd.org
- OSV CVE-2026-104426 osv.dev
- CVE-2026-104426 on threatint cve.threatint.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 17:23.
Original description (NVD)
Zebra before 6.1.0 contains an inefficient algorithmic complexity vulnerability in remaining_transaction_value that clones the entire block-level spent-UTXO map per transaction during contextual verification. Attackers can mine or seed the mempool with roughly 26,000 minimal single-input transactions in one block, stalling every validating node for over 52 seconds.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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