CVE-2020-0601
Microsoft Windows CryptoAPI Spoofing Vulnerability
Description
CVE-2020-0601 is a high-severity spoofing vulnerability in the Microsoft Windows CryptoAPI (Crypt32.dll), widely known as CurveBall. The vulnerability exists in the way Windows validates Elliptic Curve Cryptography (ECC) certificates, allowing an attacker to spoof code-signing certificates and make malicious executables appear to come from trusted sources. An attacker could also conduct man-in-the-middle attacks to decrypt confidential information on user connections. This improper certificate validation flaw affects Windows 10 and Windows Server editions. CISA has issued Emergency Directive 20-02 for this vulnerability and added CVE-2020-0601 to its Known Exploited Vulnerabilities catalog. The EPSS score of 94.1% (99.9th percentile) indicates near-certain exploitation activity.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:NOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 10 1507 | - |
| microsoft | windows 10 1607 | - |
| microsoft | windows 10 1709 | - |
| microsoft | windows 10 1803 | - |
| microsoft | windows 10 1809 | All versions |
| microsoft | windows 10 1903 | - |
| microsoft | windows 10 1909 | - |
| microsoft | windows server 1803 | - |
| microsoft | windows server 1903 | - |
| microsoft | windows server 1909 | - |
| microsoft | windows server 2016 | - |
| microsoft | windows server 2019 | - |
| golang | go | >= 1.12, < 1.12.16; >= 1.13, < 1.13.7 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
References
- http://packetstormsecurity.com/files/155960/CurveBall-Microsoft-Windows-CryptoAPI-Spoofing-Proof-Of-Concept.html(Third Party Advisory, VDB Entry)
- http://packetstormsecurity.com/files/155961/CurveBall-Microsoft-Windows-CryptoAPI-Spoofing-Proof-Of-Concept.html(Third Party Advisory, VDB Entry)
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0601(Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0601(US Government Resource)
Weakness Type
CWE-295: Improper Certificate Validation
Improper certificate validation occurs when software fails to properly verify the identity of a remote host through certificate checks. In CVE-2020-0601, the Windows CryptoAPI does not correctly validate ECC certificate parameters, allowing an attacker to craft certificates with spoofed trust chains that bypass Windows certificate verification, undermining the entire code-signing and TLS trust model.
Learn more: CWE-295 — Improper Certificate Validation
Impact Analysis
CVE-2020-0601 carries a CVSS 3.1 score of 8.1 (HIGH), reflecting the severe trust implications of a cryptographic spoofing vulnerability. The vulnerability is remotely exploitable over the network with low attack complexity, though user interaction is required. No authentication is needed to exploit this flaw. Confidentiality (High): an attacker can perform man-in-the-middle attacks to intercept and decrypt TLS-protected communications, exposing sensitive data in transit. Integrity (High): by spoofing code-signing certificates, an attacker can make malicious software appear legitimately signed, bypassing trust-based security controls and potentially compromising software supply chains. Availability (None): the CVSS assessment indicates no direct availability impact. The EPSS score of 94.1% (99.9th percentile) indicates near-certain exploitation, and the fundamental nature of this cryptographic flaw undermines Windows certificate trust at the operating system level.
Exploit Maturity
CVE-2020-0601 has a highly mature exploit landscape with confirmed active exploitation. Proof-of-concept exploit code is available through multiple sources on Packet Storm Security, demonstrating the CurveBall certificate spoofing technique. CISA has confirmed active exploitation and issued Emergency Directive 20-02 specifically for this vulnerability, underscoring its severity. The EPSS score of 94.1% (99.9th percentile) indicates near-certain exploitation activity. The fundamental nature of this cryptographic flaw makes it particularly dangerous, as it can be used to bypass code-signing verification, spoof HTTPS websites, and conduct man-in-the-middle attacks on encrypted communications.
Remediation
- Apply Microsoft security updates immediately as mandated by CISA Emergency Directive 20-02: Apply updates per vendor instructions. Patches are available through the Microsoft Security Response Center.
- Verify that all affected systems are patched, including Windows 10 (versions 1507, 1607, 1709, 1803, 1809, 1903, 1909), Windows Server 2016, Windows Server 2019, and Windows Server SAC releases (1803, 1903, 1909). Additionally, update Go language installations to version 1.12.16 or 1.13.7 or later.
- Enable and monitor Windows Event Log entries for CryptoAPI certificate validation events (Event IDs 1 from source Audit-CVE). Microsoft released a detection mechanism that logs exploitation attempts after the patch is applied.
- Review and validate all recently installed software and code-signing certificates to ensure no spoofed certificates have been used to install malicious software during the vulnerability window.
- Deploy network monitoring to detect potential man-in-the-middle attacks, particularly anomalous TLS certificate presentations with unusual ECC parameters. Review TLS inspection logs for certificates that may have exploited the CurveBall vulnerability.
Technical Details
CVE-2020-0601 is an improper certificate validation vulnerability in the Windows CryptoAPI (Crypt32.dll) that affects how ECC certificates are verified. The flaw lies in the CryptoAPI's failure to properly validate the explicit curve parameters of ECC certificates. An attacker can craft a certificate that specifies custom ECC parameters which generate a public key that appears to chain to a trusted root certificate authority, even though it is controlled by the attacker. The CVSS vector (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N) indicates network-based exploitation with low complexity and no privileges required, though user interaction is needed. This vulnerability fundamentally undermines the Windows certificate trust model, as any code-signed binary or TLS certificate validated through CryptoAPI can be spoofed.
Frequently Asked Questions
Is CVE-2020-0601 being actively exploited?
Yes. CVE-2020-0601 is listed in the CISA Known Exploited Vulnerabilities catalog with confirmed active exploitation, and CISA issued Emergency Directive 20-02 specifically addressing this vulnerability. The EPSS score of 94.1% (99.9th percentile) indicates near-certain exploitation activity. Multiple proof-of-concept exploits are publicly available.
What products are affected by CVE-2020-0601?
CVE-2020-0601 affects Microsoft Windows 10 (versions 1507, 1607, 1709, 1803, 1809, 1903, 1909), Windows Server 2016, Windows Server 2019, and Windows Server SAC releases (1803, 1903, 1909). Additionally, Go language versions 1.12 to 1.12.15 and 1.13 to 1.13.6 are also affected.
How do I fix CVE-2020-0601?
Apply Microsoft security updates as mandated by CISA Emergency Directive 20-02. Ensure all affected Windows systems and Go installations are updated. After patching, enable CryptoAPI audit logging to detect any prior exploitation attempts and review recently installed software for potentially spoofed code-signing certificates.
How severe is CVE-2020-0601?
CVE-2020-0601 has a CVSS 3.1 score of 8.1 (HIGH). This cryptographic spoofing vulnerability undermines the fundamental trust model of Windows certificate validation. With an EPSS score of 94.1% in the 99.9th percentile and a dedicated CISA Emergency Directive, this vulnerability requires immediate remediation.
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