Zebra before 7.0.0 Sync Denial of Service via Forged Checkpoint Block Body
Affects zebrad 6.4.2 and earlier, and 7.0.0-rc.0, when syncing from scratch or resyncing within about 3,000 blocks of the final checkpoint with checkpoint_sync enabled (the default). Fixed in 7.0.0.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 7.0.0
- Who is exposed
- Default setups
Do first: Check every install: default setups are affected.
- Last modified
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.34% · 28th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 31/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Default setups
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Zebra before 7.0.0 contains an incomplete cleanup vulnerability that allows unauthenticated peers to stall initial sync by serving a forged checkpoint block body. Attackers can supply a body with forged authorizing data near the final checkpoint, leaving rejected hashes in the sent-hash set so the node stops requesting blocks until restart.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure22/25Default setups, reachable over the network without a login
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
What to do
Check every install: default setups are affected.
Upgrade to a fixed version: 7.0.0.
Workaround: Restart the node when sync stops advancing during initial sync near the final checkpoint
Timeline
- CVE published
- First seen by cve.now
Affected versions
- ZcashFoundation zebra
fixed in 7.0.0
Evidence 2
- Advisory
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123560
Is CVE-2026-123560 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: cve.now feed data
What does this mean?
A peer that does not need to authenticate can send a forged checkpoint block body that halts ordinary P2P initial sync in the affected node process until it is restarted. The advisory states that no invalid state is persisted, no fork occurs, and no funds are affected.Source: github.com
Which versions are affected by CVE-2026-123560?
zebra: before 7.0.0.Source: cve.now feed data
Am I affected, and how do I check?
Affected zebrad versions are 6.4.2 or earlier, and 7.0.0-rc.0. The bug applies when checkpoint_sync is enabled (the default) and the node is syncing from scratch or resyncing, within about 3,000 blocks below the final compiled checkpoint. To check, look at the zebrad version in use and the checkpoint_sync setting in the config file.Source: github.com
How do I fix CVE-2026-123560?
Upgrade to zebrad 7.0.0, which contains the fix. Until then, if sync stops advancing during initial sync near the final checkpoint, restart the node.Source: github.com