CVE-2020-26939

Observable Differences in Behavior to Error Inputs in Bouncy Castle

In Legion of the Bouncy Castle BC before 1.55 and BC-FJA before 1.0.2, attackers can obtain sensitive information about a private exponent because of Observable Differences in Behavior to Error Inputs. This occurs in org.bouncycastle.crypto.encodings.OAEPEncoding. Sending invalid ciphertext that decrypts to a short payload in the OAEP Decoder could result in the throwing of an early exception, potentially leaking some information about the private exponent of the RSA private key performing the encryption.

CVE-2020-26939 has a CVSS score of 5.3 (Medium). 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 (1.61, 1.0.2); upgrading removes the vulnerable code path.

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1. What is CVE-2020-26939? CVE-2020-26939 is a medium-severity security vulnerability in org.bouncycastle:bcprov-jdk14 (maven), affecting versions < 1.61. It is fixed in 1.61, 1.0.2.
2. How severe is CVE-2020-26939? CVE-2020-26939 has a CVSS score of 5.3 (Medium). 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.
3. Which packages are affected by CVE-2020-26939?
   • org.bouncycastle:bcprov-jdk14 (maven) (versions < 1.61)
   • org.bouncycastle:bcprov-jdk15 (maven) (versions < 1.61)
   • org.bouncycastle:bcprov-jdk16 (maven) (versions < 1.61)
   • org.bouncycastle:bc-fips (maven) (versions < 1.0.2)
   • org.bouncycastle:bcprov-ext-jdk15on (maven) (versions < 1.61)
   • org.bouncycastle:bcprov-ext-jdk16 (maven) (versions < 1.61)
   • org.bouncycastle:bcprov-jdk15on (maven) (versions < 1.61)
   • org.bouncycastle:bcprov-jdk15to18 (maven) (versions < 1.61)
4. Is there a fix for CVE-2020-26939? Yes. CVE-2020-26939 is fixed in 1.61, 1.0.2. Upgrade to this version or later.
5. Is CVE-2020-26939 exploitable, and should I be worried? Whether CVE-2020-26939 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
6. What actually determines whether CVE-2020-26939 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.
7. How do I fix CVE-2020-26939?
   • Upgrade org.bouncycastle:bcprov-jdk14 to 1.61 or later
   • Upgrade org.bouncycastle:bcprov-jdk15 to 1.61 or later
   • Upgrade org.bouncycastle:bcprov-jdk16 to 1.61 or later
   • Upgrade org.bouncycastle:bc-fips to 1.0.2 or later
   • Upgrade org.bouncycastle:bcprov-ext-jdk15on to 1.61 or later
   • Upgrade org.bouncycastle:bcprov-ext-jdk16 to 1.61 or later
   • Upgrade org.bouncycastle:bcprov-jdk15on to 1.61 or later
   • Upgrade org.bouncycastle:bcprov-jdk15to18 to 1.61 or later

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