ZEBRA: Mempool transaction admission denial via single-peer inbound queue saturation
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · Low
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-770.
Summary
ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, one unauthenticated P2P peer can monopolize all 25 MAX_INBOUND_CONCURRENCY slots in Zebra's inbound mempool download and verification pipeline. In zebrad/src/components/mempool/downloads.rs, the bounded queue was shared globally without per-peer accounting, while peer identity was not carried through Gossip and FullQueue responses were mapped to Response::Nil instead of reaching overload disconnection handling. An attacker can advertise fake transaction identifiers and remain silent so each task holds a slot until TRANSACTION_DOWNLOAD_TIMEOUT, then periodically refill the queue as slots expire. While saturated, honest peer transactions and local sendrawtransaction requests are rejected with MempoolError::FullQueue, although block validation and synchronization continue. This issue is fixed in version 4.5.0.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| ZcashFoundation | zebra | before 4.5.0 | 4.5.0 | Patch available | CNA |
| — | zebrad (crates.io) | before 4.5.0 | 4.5.0 | Patch available | GHSA-4fc2-h7jh-287c |
- zebra VendorZcashFoundation Affected before 4.5.0 Fixed in 4.5.0 Patch available CNA
- zebrad (crates.io) Vendor— Affected before 4.5.0 Fixed in 4.5.0 Patch available GHSA-4fc2-h7jh-287c
Remediation
- Fix · CNA zebra (ZcashFoundation) Fixed in 4.5.0
- Fix · GHSA-4fc2-h7jh-287c zebrad (crates.io) Fixed in 4.5.0 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-52732
- 2026-10-03 Alias added: GHSA-4fc2-h7jh-287c
References
Other 5
- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-4fc2-h7jh-287c
- https://github.com/ZcashFoundation/zebra/commit/1440b43ca7df59aca948090d45117557b217a6cd
- https://github.com/ZcashFoundation/zebra/releases/tag/v4.5.0
- https://github.com/ZcashFoundation/zebra
- https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/zebrad/src/components/mempool/downloads.rs#L82
More ZcashFoundation vulnerabilities
- TI-2026-66079 Zebra before 4.4.0 Consensus Split via SIGHASH_SINGLE Missing-Output Handling CVSS 4.0HIGH 8.3
- TI-2026-71182 Improper block validation in Zebra gossip lets peers drop new blocks CVSS 4.0MEDIUM 6.3
- TI-2026-29537 Zebra: addr/addrv2 Deserialization Resource Exhaustion CVSS 4.0MEDIUM 6.3
- TI-2026-86702 Incomplete cleanup in Zebra lets peers stall initial sync CVSS 4.0HIGH 8.7
- TI-2026-86701 Quadratic signature hashing in Zcash Zebra enables denial of service CVSS 4.0HIGH 8.7
- TI-2026-86700 Improper cleanup stalls Zebra checkpoint sync via a malicious peer CVSS 4.0HIGH 8.7
Sources
- CVE-2026-52732 · CVE Program
- CVE-2026-52732 · NVD
- FIRST EPSS
- GHSA-4fc2-h7jh-287c · GitHub Advisory Database · CC BY 4.0
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