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CVE-2026-52732: ZEBRA: Mempool transaction admission denial via single-peer inbound queue saturation

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-18 · updated 2026-10-22
• Weakness: CWE-770

Description

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.

Affected products

• ZcashFoundation zebra: before 4.5.0

References

• https://github.com/ZcashFoundation/zebra/commit/1440b43ca7df59aca948090d45117557b217a6cd
• https://github.com/ZcashFoundation/zebra/releases/tag/v4.5.0
• https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-4fc2-h7jh-287c
• https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-4fc2-h7jh-287c

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