CVE-2026-46369 is a high-severity (CVSS 7.5) vulnerability in nimiq-blockchain. O3 Security confirms whether CVE-2026-46369 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
nimiq-blockchain: Validity store off by one error
Real-World Exposure
nimiq-blockchainReal-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
Impact
The validity store treats a transaction with stored block_number = X as "in window" only when X > last_bn - transaction_validity_window_blocks (strict inequality). However the protocol's Transaction::is_valid_at accepts a transaction for inclusion in any block in [validity_start_height - blocks_per_batch, validity_start_height + window - 1]. By choosing validity_start_height = X + blocks_per_batch (the largest value still compatible with first inclusion at block X), an attacker can replay the same signed transaction in any block B such that X + window < B < validity_start_height + window, i.e., a contiguous window of blocks_per_batch - 1 blocks (59 on MainNet, ~10 minutes) during which the replay-protection check fails to flag it. The same transaction is then executed twice: the sender is debited twice, the recipient credited twice.
Patches
https://github.com/nimiq/core-rs-albatross/pull/3772
Workarounds
No known workarounds
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | nimiq-blockchain | all versions | 1.5.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nimiq-blockchain. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update nimiq-blockchain to 1.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-46369 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 pinpoints whether CVE-2026-46369 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-46369. 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-2026-46369 in your dependencies?
O3 detects CVE-2026-46369 across crates.io dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.