CVE-2025-20339
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 · uneditedA vulnerability in the access control list (ACL) processing of IPv4 packets of Cisco SD-WAN vEdge Software could allow an unauthenticated, remote attacker to bypass a configured ACL. This vulnerability is due to the improper enforcement of the implicit deny all at the end of a configured ACL. An attacker could exploit this vulnerability by attempting to send unauthorized traffic to an interface on an affected device. A successful exploit could allow the attacker to bypass an ACL on the affected device.
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 vulnerability in Cisco SD-WAN vEdge Software involves improper enforcement of the implicit deny all rule at the end of IPv4 ACLs. The ACL processing logic fails to implicitly deny traffic that doesn't match any explicit ACL entries, allowing unauthorized traffic to bypass configured ACLs. An attacker can send traffic to an affected device interface that should be blocked but will be permitted.
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
- Changed
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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.
-
Identify device and versionRun 'show version' or 'show software' command on the Cisco SD-WAN vEdge device to obtain the installed software version.Affected if The device runs Cisco SD-WAN vEdge Software and the version falls within the affected range (compare your installed version to known affected versions).
-
Confirm IPv4 ACL configurationRun 'show access-lists' or 'show configuration | match access-list' to list all configured IPv4 access control lists on the device.Affected if IPv4 ACLs are configured on any interface (the vulnerability affects ACL processing regardless of which interface).
-
Check ACL entries and implicit deny behaviorRun 'show access-list <acl-name>' to view detailed ACL entries. Use 'show platform hardware qfp active feature acl' or similar platform commands to verify ACL processing behavior and whether implicit deny is being enforced.Affected if The ACL contains entries but traffic not matching any explicit entry appears to be permitted instead of denied (test with traffic that should be blocked).
-
Test implicit deny enforcementConfigure a test ACL with specific permit entries and send traffic destined for IPs/networks not covered by any explicit permit statement. Use 'show access-list statistics' or packet capture to observe whether unmatched traffic is being dropped.Affected if Unmatched traffic passes through when it should be implicitly denied by the ACL.
A defender is affected if running vulnerable Cisco SD-WAN vEdge Software with configured IPv4 ACLs where traffic that does not match any explicit ACL entry is permitted instead of being denied.
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 the Cisco software update addressing CVE-2025-20339 when available. Until then, implement additional compensating controls such as stricter edge filtering or alternative firewall mechanisms.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,096.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-20339 — 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-2025-20339 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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
- No spam, self-promotion, credentials, or personal data