Summary
Workarounds
Do strict ASN.1 DER checking for ASN.1 encoded ECDSA signature value.
References
https://nvd.nist.gov/vuln/detail/CVE-2020-14966
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-14966
https://vuldb.com/?id.157123
https://github.com/kjur/jsrsasign/issues/437
https://kjur.github.io/jsrsasign/api/symbols/KJUR.crypto.ECDSA.html
https://kjur.github.io/jsrsasign/api/symbols/ASN1HEX.html#.checkStrictDER
https://www.itu.int/rec/T-REC-X.690
Impact
Jsrsasign supports ECDSA signature validation which signature value is represented by ASN.1 DER encoding. This vulnerablity may accept a wrong ASN.1 DER encoded ECDSA signature such as:
- wrong multi-byte ASN.1 length of TLV (ex. 0x820045 even though 0x45 is correct)
- prepending zeros with ASN.1 INTEGER value (ex. 0x00000123 even though 0x0123 is correct)
- appending zeros to signature of ASN.1 TLV (ex. 0x3082....1fbc000000 even though 0x3082....1fbc, appending zeros are ignored.)
This vulnerability was fixed by strict ASN.1 DER checking.
Here is an assessment of this vulnerability:
- If you are not use ECDSA signature validation, this vulnerability is not affected.
- Not ASN.1 format signature like just concatenation of R and S value is not affected such as Bitcoin.
- This vulnerability is affected to all ECC curve parameters.
- Risk to accept a forged or crafted message to be signed is low.
- Risk to raise memory corruption is low since jsrsasign uses BigInteger class.
- ECDSA signatures semantically the same to valid one may be accepted as valid. There are many malleable variants.
As discussed here, there is no standards like X9.62 which requires ASN.1 DER. So ASN.1 BER can be applied to ECDSA however most of implementations like OpenSSL do strict ASN.1 DER checking.
CVE-2020-14966 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (8.0.19); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Users using ECDSA signature validation should upgrade to 8.0.19.
Frequently Asked Questions
- What is CVE-2020-14966? CVE-2020-14966 is a high-severity security vulnerability in jsrsasign (npm), affecting versions >= 4.0.0, < 8.0.19. It is fixed in 8.0.19.
- How severe is CVE-2020-14966? CVE-2020-14966 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of jsrsasign are affected by CVE-2020-14966? jsrsasign (npm) versions >= 4.0.0, < 8.0.19 is affected.
- Is there a fix for CVE-2020-14966? Yes. CVE-2020-14966 is fixed in 8.0.19. Upgrade to this version or later.
- Is CVE-2020-14966 exploitable, and should I be worried? Whether CVE-2020-14966 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-14966 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-14966? Upgrade
jsrsasignto 8.0.19 or later.