CVE-2026-90975VulnerabilityPublished 26 Oct 2026

VU#701544: mpc-lib Hardened Derivation Fails to Protect Ancestor Isolation

Source CERT/CC

Not known to be exploited.

Data as of 27 Oct 2026, 00:12 UTC

Severity

High

Rated High by Threat Radar's AI analysis · CVSS not yet scored by NVD

Exploitation evidence

Disclosed: evidence found.
Public on cve.org; its publication date is not in this record
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

No vendor fix is currently available. The most effective mitigation is to treat the chain code as secret and avoid exposing it in watch-only extended public keys or to untrusted parties, as the attack requires knowledge of the chain code. Additionally, integrators should not rely solely on hardened derivation for isolation between signer shares and should audit derivation paths for hardened segments. Compromise of any single share should be treated as potentially exposing other shares across the derivation hierarchy. A complete fix requires a code change in the mpc-lib library.

Description

Fireblocks' mpc-lib library has a cryptographic fail-open vulnerability in its BIP32 hardened derivation implementation when the private parent key is missing. This flaw breaks the ancestor isolation property, allowing an attacker with a compromised lower-level signer share and knowledge of the chain code to recover higher-level shares up to the root share. The primary MPC secret-sharing layer still prevents full private key reconstruction from a single share compromise, but the hardened derivation no longer provides defense-in-depth isolation between derivation levels. No vendor fix is currently available, and mitigation involves keeping the chain code secret and auditing derivation paths.

Impact

An attacker with access to a compromised lower-level signer share and knowledge of the chain code can recover ancestor shares up to the root share for that MPC party. This breaks the hardened derivation's ancestor isolation property, allowing compromise to propagate across derivation levels. However, the primary MPC secret-sharing mechanism still prevents reconstruction of a full private key from a single compromised share, so the vulnerability does not directly yield a spendable key. The flaw silently downgrades security assumptions and eliminates a defense-in-depth layer, increasing risk over time as compromise can extend across the key hierarchy.

References

kb.cert.org/vuls/id/701544 (opens in a new tab)

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