CVE-2025-56233
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 · uneditedOpenindiana, kernel SunOS 5.11 has a denial of service vulnerability. For the processing of TCP packets with RST or SYN flag set, Openindiana has a wide acceptable range of sequence numbers. It does not require the sequence number to exactly match the next expected sequence value, just to be within the current receive window, which violates RFC5961. This flaw allows attackers to send multiple random TCP RST/SYN packets to hit the acceptable range of sequence numbers, thereby interrupting normal connections and causing a denial of service attack.
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 confidenceOpenindiana SunOS 5.11 kernel has a flaw in TCP packet processing where RST and SYN packets are accepted with any sequence number within the current receive window, rather than requiring an exact match to the next expected sequence value as specified by RFC5961. Attackers can exploit this by sending random TCP RST/SYN packets with varying sequence numbers until they fall within the acceptable window, causing legitimate connections to be terminated and resulting in denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS 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
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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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Confirm Openindiana SunOS 5.11 installationRun 'uname -a' or 'cat /etc/release' to identify the operating system and versionAffected if The system is running Openindiana SunOS 5.11 (any kernel build)
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Identify kernel versionRun 'uname -v' to obtain the kernel build versionAffected if Kernel version is any build of SunOS 5.11 on Openindiana
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Determine TCP exposureReview network configuration using 'netstat -an' or 'ipadm show-prop -p tcp tcp' to identify listening TCP services and their exposure to untrusted networksAffected if The system has TCP services (such as SSH, HTTP, or other network listeners) accessible from untrusted or internet-facing networks
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Check for connection anomaliesMonitor system logs (/var/adm/messages) and use 'netstat -s' to look for spikes in TCP connection resets or unexpected disconnectionsAffected if There is a sudden increase in TCP RST packets or legitimate connections are being dropped unexpectedly
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Verify RFC5961 compliance (if tooling available)Use a packet capture tool (such as tcpdump) to inspect incoming TCP RST and SYN packets and verify if any are being accepted with sequence numbers outside the exact expected valueAffected if TCP RST or SYN packets with sequence numbers within (but not matching) the receive window are being accepted by the kernel
A system is affected if it runs Openindiana SunOS 5.11 with any TCP services exposed to untrusted networks, as the kernel accepts TCP RST/SYN packets with any sequence number within the receive window instead of requiring exact matches per RFC5961.
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 dataApply vendor patches for Openindiana to address the RFC5961 violation in TCP sequence number validation; until a patch is available, consider network-level mitigations such as TCP connection tracking, rate limiting, or filtering suspicious RST/SYN packets.
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-56233 — 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-2025-56233 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
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