CVE-2020-27635
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 · uneditedIn PicoTCP 1.7.0, TCP ISNs are improperly random.
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 confidenceIn PicoTCP 1.7.0, the TCP Initial Sequence Number (ISN) generation uses insufficient randomness, making ISNs predictable. This allows remote attackers to perform TCP sequence number prediction attacks, potentially enabling session hijacking, connection spoofing, or man-in-the-middle attacks against TCP connections.
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= 1.7.0CVSS 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
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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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Identify if PicoTCP is in useSearch for PicoTCP library files, check product documentation, or examine software Bill of Materials (SBOM) for 'picotcp' or 'PicoTCP' componentsAffected if PicoTCP library is present in the environment
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Determine the installed PicoTCP versionCheck version information via library file metadata, product version strings, or firmware/system inventory that lists the picotcp component versionAffected if The version is exactly 1.7.0
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Verify TCP protocol support is enabledExamine the PicoTCP build configuration or runtime settings to confirm TCP networking stack is compiled and activeAffected if TCP support is enabled and the system accepts TCP connections
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Confirm ISN generation uses weak randomnessReview source code or binary configuration for the ISN generation function (typically in tcp.c or isn.c) to verify it uses a predictable algorithm rather than a cryptographically secure random number generatorAffected if The ISN generation code uses non-crypto random sources like simple PRNG, time-based values, or counters
The environment is affected if PicoTCP version 1.7.0 is deployed and TCP networking is enabled, allowing attackers to predict sequence numbers for TCP connection hijacking or spoofing.
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 existing ISN generation mechanism with a cryptographically secure random number generator (CSPRNG) that produces unpredictable sequence numbers. If a patched version of PicoTCP is available, upgrade to that version.
- Consultation2.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-27635 — 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-2020-27635 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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