Zebra has sync restart poisoning from single unauthenticated peer via above-lookahead block

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-52737: 0.26% estimated exploitation activity in the next 30 days; percentile 18.11 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Am I affected You are affected if: 1. You run zebrad up to and including v4.4.1. 2. Your node accepts inbound P2P connections and is syncing or catching up to the chain tip. Summary A malicious peer can answer Zebra's outbound getblocks/FindBlocks request with a small two-hash inventory, then serve a syntactically valid block whose coinbase height is far above the victim's local tip. The AboveLookaheadHeightLimit error in the sync download pipeline triggers a global sync restart rather than being scoped to the offending peer. The peer is never scored or disconnected because the error type does not carry the advertiser address. On mainnet, each successful cycle imposes a 67-second sync restart delay. All in-flight downloads from honest peers are cancelled on each restart. Details The bug is the interaction of three layers: 1. The syncer promotes unvalidated FindBlocks peer responses into concrete download schedules without checking that the advertised hashes are plausible chain…

Published by the source

2 Jul 2026, 19:44 UTC

Last modified by the source

2 Jul 2026, 19:44 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-gvjc-3w7c-92jx

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# Patch Next advisory brief: CVE-2026-52737

Advisory: Zebra has sync restart poisoning from single unauthenticated peer via above-lookahead block
IDs: CVE-2026-52737, GHSA-gvjc-3w7c-92jx
Record: https://patchnext.com/advisories/cve-2026-52737 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: zebra-consensus 7.0.0; zebrad 4.5.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io zebra-consensus: affected <= 6.0.0; fixed in 7.0.0
- crates.io zebrad: affected <= 4.4.1; fixed in 4.5.0

## Suggested inspection (read-only)
- crates.io zebra-consensus: check the installed version with your package manager.
- crates.io zebrad: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on zebra-consensus, zebrad.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-gvjc-3w7c-92jx (GitHub-reviewed advisory GHSA-gvjc-3w7c-92jx lists affected ranges: crates.io zebra-consensus >=0 =0 <=4.4.1)

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