CVE-2026-40093: nimiq-blockchain is missing a wall-clock upper bound on block timestamps

Should you act?

Normal patch cycle

No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.4%, percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes nimiq-blockchain (crates.io (Rust)) <= 1.3.0, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

nimiq-blockchain provides persistent block storage for Nimiq's Rust implementation. In 1.3.0 and earlier, block timestamp validation enforces that timestamp >= parent.timestamp for non-skip blocks and timestamp == parent.timestamp + MINPRODUCERTIMEOUT for skip blocks, but there is no visible upper bound check against the wall clock. A malicious block-producing validator can set block timestamps arbitrarily far in the future. This directly affects reward calculations via Policy::supplyat() and batchdelay() in blockchain/src/reward.rs, inflating the monetary supply beyond the intended emission schedule.

From the GitHub advisory

Impact

Block timestamp validation enforces that timestamp >= parent.timestamp for non-skip blocks and timestamp == parent.timestamp + MINPRODUCERTIMEOUT for skip blocks, but there is no visible upper bound check against the wall clock. A malicious block-producing validator can set block timestamps arbitrarily far in the future. This directly affects reward calculations via Policy::supplyat() and batchdelay() in blockchain/src/reward.rs, inflating the monetary supply beyond the intended emission schedule.

Patches TBD

Workarounds No know workarounds.

Weakness type: CWE-1284, CWE-20.

Product: nimiq-blockchain (crates.io (Rust)) · Assigned by: GitHub_M · Published: 2026-04-09

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.43% probability of exploitation activity in the next 30 days; percentile 37.

Timeline

• 2026-04-09 — CVE record published by GitHub_M
• 2026-04-10 — GitHub-reviewed advisory GHSA-49xc-52mp-cc9j published (critical)
• 2026-04-13 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-49xc-52mp-cc9j github.com
2. CVE.org record CVE-2026-40093 cve.org
3. NVD entry CVE-2026-40093 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

Critical crates.io (Rust) advisories · Today’s Security Digest