GHSA-4fc2-h7jh-287c — zebrad
MEDIUMGHSA-4fc2-h7jh-287c is a medium-severity (CVSS 5.3) CWE-770 vulnerability in zebrad. A fix is available for zebrad — see the affected versions and patch details below.
zebrad has mempool transaction admission denial via single-peer inbound queue saturation
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-4fc2-h7jh-287c.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-4fc2-h7jh-287c plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
zebradReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Am I affected
You are affected if:
- You run
zebradup to and includingv4.4.1. - Your node accepts inbound P2P connections (
network.listen_addris set, which is the default). - Your node's mempool is active (node is synced near the chain tip).
All default configurations are affected.
Summary
A single unauthenticated P2P peer can monopolize all 25 inbound mempool download/verification slots (MAX_INBOUND_CONCURRENCY) by advertising fake transaction IDs. While the slots are occupied, all other inbound transactions from honest peers and local RPC sendrawtransaction calls are rejected with MempoolError::FullQueue. The attacker peer is never scored for misbehavior and is not disconnected, allowing sustained denial of mempool admission.
Details
The mempool download/verification pipeline at zebrad/src/components/mempool/downloads.rs uses a single bounded pool of 25 concurrent tasks. Three architectural gaps combine to produce the vulnerability:
- No per-peer accounting: the 25 slots are shared across all peers with no cap on how many a single peer can hold.
- No overload signaling: when
FullQueueis returned, the inbound service atzebrad/src/components/inbound.rsmaps it toResponse::Nil, hiding the overload from the peer connection layer. The existinghandle_inbound_overloaddisconnection logic never fires. - No misbehavior attribution: peer identity is not carried through the
Gossiptype into the download pipeline, so verification failures cannot be attributed to the originating peer.
The attacker sends inv messages advertising fake transaction IDs. Zebra queues download tasks for each ID. The attacker stays silent; each slot is held until the TRANSACTION_DOWNLOAD_TIMEOUT (20 seconds) fires. The attacker periodically sends fresh inv waves to re-fill slots as they expire.
Two additional slot-holding techniques have been independently demonstrated: invalid-prevout transactions that park in AwaitOutput for 60 seconds, and expensive shielded proof verification with auth-variant cache bypass. All three techniques are addressed by the same per-peer accounting fix.
Patches
zebrad 4.5.0
The fix adds per-peer queue accounting to the mempool download pipeline. A single peer is limited to a fraction of MAX_INBOUND_CONCURRENCY (e.g., 5 slots out of 25). FullQueue is surfaced as an overload signal to the peer connection layer. Peer identity is plumbed through the Gossip type for misbehavior attribution.
Workarounds
There is no complete configuration-level workaround. Reducing network.peerset_initial_target_size limits the total inbound peer count but does not prevent a single peer from holding all mempool slots.
Impact
Mempool transaction admission is denied for all honest peers and local RPC clients while the attack is sustained. Block validation and chain synchronization continue normally. The attacker needs only one TCP connection and minimal bandwidth (~1 KB/s of fake inv messages). The node recovers immediately when the attacker stops. This does not affect consensus, funds, or on-disk state.
Credit
Reported by @dingledropper via a private GitHub Security Advisory submission.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | zebrad | all versions | 4.5.0cargo update -p zebrad --precise 4.5.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for zebrad, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update zebrad to 4.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4fc2-h7jh-287c is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-4fc2-h7jh-287c can be triaged on real exposure rather than presence alone.
Tailored to GHSA-4fc2-h7jh-287c. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-4fc2-h7jh-287c in your dependencies?
O3 Security finds GHSA-4fc2-h7jh-287c across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.