CVE-2020-27631
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 Oryx CycloneTCP 1.9.6, 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 · moderate confidenceIn Oryx CycloneTCP 1.9.6, the TCP Initial Sequence Number (ISN) generation is insufficiently randomized, making TCP session prediction feasible. Predictable ISNs allow remote attackers to perform TCP spoofing or session hijacking attacks by anticipating sequence numbers.
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= 1.9.6CVSS 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
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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 CycloneTCP installationSearch your system for CycloneTCP libraries, headers, or any software that embeds Oryx CycloneTCP. Check project dependencies, firmware components, or embedded system manifests for 'CycloneTCP' or 'oryx' references.Affected if CycloneTCP version 1.9.6 is present in your environment
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Determine CycloneTCP versionReview your software bill of materials (BOM), firmware version records, or library inventory to confirm the exact CycloneTCP version. Check version strings in compiled binaries if available.Affected if The installed version is exactly 1.9.6
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Verify TCP stack is enabledCheck your CycloneTCP configuration (typically in cyclonetcp_config.h or similar header) for NET_TCP_MODULE_ENABLED or TCP_ENABLED define. Confirm TCP is compiled into the build.Affected if TCP module is enabled in the CycloneTCP configuration
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Check for active TCP listening servicesReview your system or device to determine if any TCP servers, listeners, or client connections are configured. This includes web servers, telnet, SSH, or any custom TCP-based services using CycloneTCP.Affected if The device or application accepts or initiates TCP connections using the affected CycloneTCP stack
You are affected if CycloneTCP version 1.9.6 is in use and the TCP stack is enabled, as the predictable ISN affects all TCP sessions established by this version.
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 dataUpgrade to a patched version of CycloneTCP that implements cryptographically secure ISN generation, or contact Oryx for vendor-supplied patches.
- Consultation2.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,536.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-27631 — 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-2020-27631 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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