CVE-2026-1229

Critical

Published: 24 February 2026

Published

24 February 2026

Modified

03 March 2026

KEV Added

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Patch

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CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0002 6.5th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-1229 is a critical-severity Incorrect Calculation (CWE-682) vulnerability in Cloudflare Circl. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 6.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 CM-10 (Software Usage Restrictions) and RA-5 (Vulnerability Monitoring and Scanning).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

preventrecover

Directly mandates identification, reporting, and correction of software flaws like the faulty CombinedMult function in CIRCL ecc/p384 by updating to v1.6.3 or later.

RA-5 Vulnerability Monitoring and Scanning good match

detect

Enables ongoing vulnerability scanning to identify deployments using vulnerable CIRCL library versions affected by CVE-2026-1229.

CM-10 Software Usage Restrictions good match

prevent

Restricts execution to authorized software versions, preventing use of vulnerable CIRCL ecc/p384 prior to the v1.6.3 fix.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

Remote unauthenticated exploitation of the crypto implementation flaw in a library used by public-facing applications directly matches T1190; impacts are limited to specific ECC operations and exact attacker primitives (e.g., forgery vs. DoS) are not fully detailed.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

NVD Description

The CombinedMult function in the CIRCL ecc/p384 package (secp384r1 curve) produces an incorrect value for specific inputs. The issue is fixed by using complete addition formulas. ECDH and ECDSA signing relying on this curve are not affected. The bug was…

fixed in v1.6.3 https://github.com/cloudflare/circl/releases/tag/v1.6.3 .

Deeper analysisAI

CVE-2026-1229 is a vulnerability in the CombinedMult function within the CIRCL ecc/p384 package, specifically for the secp384r1 elliptic curve. This function produces an incorrect value for certain inputs due to incomplete addition formulas. The issue affects the CIRCL library developed by Cloudflare, a Go-based cryptographic library. Notably, ECDH key exchange and ECDSA signing operations relying on this curve are not impacted.

The vulnerability carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating it can be exploited remotely by unauthenticated attackers with low complexity and no user interaction. Attackers could provide specific inputs to trigger the faulty computation in applications using the affected function, potentially leading to high impacts on confidentiality, integrity, and availability through cryptographic miscalculations.

The bug was addressed in CIRCL version 1.6.3, released with a fix implementing complete addition formulas. Additional details are available in the project's GitHub repository at https://github.com/cloudflare/circl and the specific release notes at https://github.com/cloudflare/circl/releases/tag/v1.6.3. Security practitioners should update to v1.6.3 or later to mitigate the issue.