CVE-2020-20950
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedBleichenbacher's attack on PKCS #1 v1.5 padding for RSA in Microchip Libraries for Applications 2018-11-26 All up to 2018-11-26. The vulnerability can allow one to use Bleichenbacher's oracle attack to decrypt an encrypted ciphertext by making successive queries to the server using the vulnerable library, resulting in remote information disclosure.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThis is a classic Bleichenbacher oracle attack vulnerability in the RSA PKCS#1 v1.5 padding implementation within Microchip Libraries for Applications. Attackers can decrypt RSA ciphertexts by making successive oracle queries that exploit timing differences or error message differences in the server's responses, effectively performing adaptive chosen-ciphertext attacks to gradually recover the plaintext.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 1.5<= 2018-11-26CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Locate Microchip Libraries for Applications installationSearch the system for MLA installation directories (commonly at /microchip_libraries/, /mla/, or under Program Files/Microchip on Windows). Check for a version file or manifest named version.h, version.txt, or a build date timestamp.Affected if The MLA version is dated 2018-11-26 or earlier, or no version is found but the library directory exists with RSA-related code.
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Identify RSA PKCS#1 v1.5 usage in configurationSearch project configuration files (XML, .c, .h files) for references to RSA_PKCS1_V15, RSA_PKCS1_V1_5, or explicit mentions of PKCS1 padding mode. Also check for wolfCrypt or legacy RSA API calls.Affected if RSA is configured to use PKCS#1 v1.5 padding instead of OAEP or PSS.
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Inspect RSA decryption implementation for oracle leakageExamine the RSA decryption source code in the MLA crypto library (commonly in crypto/RSA or wolfcrypt modules). Look for conditional error handling that returns different responses for padding validation failures versus other errors.Affected if The RSA decryption code returns distinct error messages or timing differences based on padding oracle conditions (e.g., 'padding check failed' vs 'invalid signature' vs 'decryption error').
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Verify error response uniformityTest or audit the RSA decryption code paths. All decryption failures (whether due to padding, key mismatch, or other causes) should return identical error codes and response times to prevent oracle leakage.Affected if Different error conditions produce different HTTP responses, error codes, or observable timing variations.
The environment is affected if Microchip Libraries for Applications version 2018-11-26 or earlier is present AND RSA PKCS#1 v1.5 padding is enabled with non-uniform error responses that could serve as a Bleichenbacher oracle.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataReplace the vulnerable RSA PKCS#1 v1.5 implementation with a constant-time implementation or migrate to OAEP padding, and ensure the server returns identical responses/timing for all decryption failures to eliminate the oracle.
- Consultation4.0 h
- Implementation16.0 h
- Testing8.0 h
- Review / QA4.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2020-20950 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2020-20950 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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