CVE-2026-104436 Zebra before 4.5.0 CPU Amplification via Uncapped getblocks/getheaders Locator Length
Remote attackers can exhaust system resources by sending oversized block locator vectors, causing denial of service in Zcash nodes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-104436?
CVE-2026-104436 is a medium-severity denial of service vulnerability in ZcashFoundation zebra, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Zebra before 4.5.0 contains an uncontrolled resource consumption vulnerability that allows remote P2P peers to exhaust blocking-pool threads by sending oversized block locator vectors. Attackers can send getblocks or getheaders messages with up to 65,535 locator hashes, triggering per-hash chain lookups that degrade block validation, RPC, and mempool performance.
Weakness: CWE-770
Which versions are affected by CVE-2026-104436?
4 open source packages ship an affected version, including zebra-chain and zebrad.
| Package | Affected | Fixed in |
|---|---|---|
zebra-chain crates.io | All versions | 8.0.0 |
zebra-chain crates.io | All versions | 8.0.0 |
zebrad crates.io | All versions | 4.5.0 |
zebrad crates.io | All versions | 4.5.0 |
How do I fix CVE-2026-104436?
Upgrade zebra-chain to 8.0.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-104436 being exploited?
There is no known exploitation of CVE-2026-104436 in the wild and no public exploit code.
Sources
Also known as GHSA-443g-gwgp-49x4, GHSA-4m38-rccq-j8gv.