CVE-2021-20048
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 Stack-based buffer overflow in the SonicOS SessionID HTTP response header allows a remote authenticated attacker to cause Denial of Service (DoS) and potentially results in code execution in the firewall. This vulnerability affected SonicOS Gen 5, Gen 6 and Gen 7 firmware versions.
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 confidenceA stack-based buffer overflow vulnerability exists in the SonicOS SessionID HTTP response header. A remote authenticated attacker can send a specially crafted HTTP response with an oversized SessionID value, causing stack memory corruption. This can lead to denial of service and potentially allow arbitrary code execution with elevated privileges on the firewall appliance.
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<= 7.0.1-r1456<= 7.0.1-5023-1349<= 7.0.1-5018-r1715<= 6.5.4.8<= 6.5.1.13-1n<= 6.0.5.3-94o<= 5.9.1.13CVSS 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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/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 the SonicOS firmware versionLog into the SonicWall management interface and navigate to System > Status, or use the CLI command 'show version' to display the current firmware version and build number.Affected if The installed version falls within any of these ranges: <= 7.0.1-r1456, <= 7.0.1-5023-1349, <= 7.0.1-5018-r1715, <= 6.5.4.8, <= 6.5.1.13-1n, <= 6.0.5.3-94o, or <= 5.9.1.13.
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Determine if HTTP management interface is enabledIn the SonicWall GUI, go to System > Administration and verify whether HTTP management access is enabled. Check both the 'Enable HTTP' and 'Enable HTTPS' settings under Management Access.Affected if HTTP management is enabled, as the vulnerability is triggered through the SessionID HTTP response header.
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Check if the management interface is accessible from untrusted networksReview the firewall access rules or NAT policies to determine if the management interface (port 80 or 443) is exposed to the internet or untrusted internal networks. Look for any NAT or access rules mapping external IPs to the SonicWall management ports.Affected if The management interface is reachable from untrusted network segments, increasing the attack surface for remote exploitation.
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Verify whether authentication is required for management accessIn System > Administration, confirm that 'Require authentication for management interface' is enabled. Also check that strong password policies are enforced for admin accounts.Affected if Authentication is disabled or weak, allowing easier exploitation by remote attackers.
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Review logs for anomalous HTTP traffic with large SessionID valuesExamine the SonicWall logs under Monitor > Log > System Logs for entries containing unusually long SessionID strings in HTTP responses, or look for crash dumps or restart events around the time of suspicious HTTP activity.Affected if Logs show abnormal HTTP response patterns with oversized SessionID values, indicating potential exploitation attempts.
The environment is affected if the SonicOS firmware version is within any of the affected version ranges AND the HTTP management interface is enabled and accessible to the attacker.
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.
dbcve · scopedApply the vendor-supplied firmware updates from SonicWall for Gen 5, Gen 6, and Gen 7 devices. If patches are not immediately available, consider network-level mitigations such as restricting management interface access to trusted IP addresses and deploying intrusion detection to monitor for anomalous HTTP traffic.
Latest SonicOS firmware for your specific model (versions beyond 7.0.1-r1456, 7.0.1-5023-1349, 7.0.1-5018-r1715, and 6.5.4.8)
- 1. Identify the exact SonicWall firewall model and current SonicOS version running on the device
- 2. Access the SonicWall support portal at psirt.global.sonicwall.com or my.sonicwall.com
- 3. Download the latest SonicOS firmware for your specific model - look for versions newer than 7.0.1 for Gen 7, and newer than the listed affected versions for Gen 5/6
- 4. Back up the current device configuration
- 5. Upload and install the new firmware via the SonicWall web management interface or CLI
- 6. Verify the upgrade was successful and restore configuration if needed
- 7. Confirm the SessionID HTTP response header behavior is corrected
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation8.0 h
- Implementation4.0 h
- Testing12.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20048 — 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-2021-20048 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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