CVE-2026-34219 — libp2p-gossipsub
MEDIUMCVE-2026-34219 is a medium-severity (CVSS 5.9) CWE-190 vulnerability in libp2p-gossipsub. A fix is available for libp2p-gossipsub — see the affected versions and patch details below.
libp2p-gossipsub: Remote crash via unchecked Instant overflow in heartbeat backoff expiry handling
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-34219.
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
CVE-2026-34219 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 378,156 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
libp2p-gossipsubReal-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
Description
Summary
The Rust libp2p Gossipsub implementation contains a remotely reachable panic in backoff expiry handling.
After a peer sends a crafted PRUNE control message with an attacker-controlled, near-maximum backoff value, the value is accepted and stored as an Instant near the representable upper bound. On a later heartbeat, the implementation performs unchecked Instant + Duration arithmetic (backoff_time + slack), which can overflow and panic with:
overflow when adding duration to instant
This issue is reachable from any Gossipsub peer over normal TCP + Noise + mplex/yamux connectivity and requires no further authentication beyond becoming a protocol peer.
Attack Scenario
An attacker that can establish a libp2p Gossipsub session with a target node can crash the target by sending crafted PRUNE control data:
- Establish a standard libp2p session (
TCP + Noise) and negotiate a stream multiplexer (mplex/yamux). - Open a Gossipsub stream and send an RPC containing
ControlPrunewith a very largebackoff(chosen near boundary conditions, e.g.~ i64::MAX - victim_uptime_seconds; example observed:9223372036854674580for ~28h uptime). - The value is parsed from protobuf and passed through
Behaviour::handle_prune()into mesh/backoff update logic. - Initial storage path uses checked addition (
Instant::now().checked_add(...)), so the malicious near-max value is retained. - On the next heartbeat (typically within ~43–74s), expiry logic computes
backoff_time + slackusing unchecked addition, which overflows and panics.
Impact
Remote unauthenticated denial of service (critical).
Any application exposing an affected libp2p-gossipsub listener can be crashed by a network-reachable peer that sends crafted PRUNE backoff values. The crash is triggered during heartbeat processing (not immediately at PRUNE parse time), and can be repeated by reconnecting and replaying the message.
Differences from CVE-2026-33040
This advisory is related to CVE-2026-33040 but it is not the same defect. CVE-2026-33040 addressed overflow during backoff insertion by adding checked arithmetic when converting PRUNE backoff into an Instant. The issue in this advisory occurs at a different location and at a different time: a near-maximum backoff can still be stored successfully, and the crash happens later in the heartbeat path when slack is added to that stored Instant using unchecked arithmetic. This report covers a distinct secondary overflow path in heartbeat expiry handling that remained reachable after the original insertion-side hardening.
This vulnerability was originally reported by the Security team of the Ethereum Foundation.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | libp2p-gossipsub | all versions | 0.49.4cargo update -p libp2p-gossipsub --precise 0.49.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for libp2p-gossipsub, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update libp2p-gossipsub to 0.49.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34219 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 CVE-2026-34219 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-34219. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-34219 in your dependencies?
O3 Security finds CVE-2026-34219 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.