# CVE-2026-52737: ZEBRA: Sync restart poisoning from single unauthenticated peer via above-lookahead block

> A malicious peer can repeatedly trigger sync restarts in Zebra nodes, causing significant synchronization delays and resource exhaustion.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Aug 2026
- **Updated:** 18 Aug 2026
- **Also known as:** GHSA-gvjc-3w7c-92jx

## What is CVE-2026-52737?

CVE-2026-52737 is a medium-severity denial of service vulnerability in ZcashFoundation zebra, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, a malicious unauthenticated P2P peer can answer Zebra's outbound getblocks or FindBlocks request with a small two-hash inventory and then serve a syntactically valid block whose coinbase height is far above the local chain tip. In zebrad/src/components/sync/downloads.rs, BlockDownloadVerifyError::AboveLookaheadHeightLimit originally carried only the block height and hash, so handle_block_response could not attribute the failure to the advertising peer. The error then reached the restart-worthy default path in zebrad/src/components/sync.rs, cancelling all in-flight downloads from honest peers and imposing a 67-second sync restart delay on mainnet. Because the peer was neither scored nor disconnected, the peer could repeat the cycle indefinitely with minimal bandwidth and significantly degrade synchronization without corrupting state. This issue is fixed in version 4.5.0.

Weakness: CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2026-52737?

4 open source packages ship an affected version, including zebra-consensus and zebrad.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `zebra-consensus` | crates.io | All versions | 7.0.0 |
| `zebra-consensus` | crates.io | All versions | 7.0.0 |
| `zebrad` | crates.io | All versions | 4.5.0 |
| `zebrad` | crates.io | All versions | 4.5.0 |

## How do I fix CVE-2026-52737?

Upgrade zebra-consensus to 7.0.0 or later.

## Is CVE-2026-52737 being exploited?

There is no known exploitation of CVE-2026-52737 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-52737 and fix it if it is affected.

What it is: CVE-2026-52737 is a medium-severity denial of service vulnerability in ZcashFoundation zebra, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-52737 in the wild and no public exploit code.

Affected packages and fixed versions:
- zebra-consensus (crates.io): affected all versions; fixed in 7.0.0
- zebra-consensus (crates.io): affected all versions; fixed in 7.0.0
- zebrad (crates.io): affected all versions; fixed in 4.5.0
- zebrad (crates.io): affected all versions; fixed in 4.5.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-52737/ (Markdown: https://insights.sbomify.com/CVE-2026-52737/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52737
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52737
- OSV: https://osv.dev/vulnerability/CVE-2026-52737

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52737/
Summaries are generated and may contain mistakes; the official description above is the record.