FedoraOperating system · Fedoraproject
CVE-2020-35503
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 NULL pointer dereference flaw was found in the megasas-gen2 SCSI host bus adapter emulation of QEMU in versions before and including 6.0. This issue occurs in the megasas_command_cancelled() callback function while dropping a SCSI request. This flaw allows a privileged guest user to crash the QEMU process on the host, resulting in a denial of service. The highest threat from this vulnerability is to system availability.
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 NULL pointer dereference vulnerability exists in QEMU's megasas-gen2 SCSI host bus adapter emulation. The flaw occurs in the megasas_command_cancelled() callback function when dropping a SCSI request, allowing a privileged guest user to crash the QEMU process on the host.
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
FedoraOperating system
= 33<= 6.0.0CVSS 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
- Local
- Complexity
- Low
- Privileges
- High
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/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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Identify installed QEMU packagesRun 'rpm -qa | grep -i qemu' (Fedora/RHEL) or check your package manager for installed qemu packagesAffected if No qemu package is installed (not affected because qemu is not in use)
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Determine QEMU versionRun 'qemu-system-x86_64 --version' or 'rpm -q qemu-kvm' or check the version of your installed qemu packageAffected if The installed version is 6.0.0 or lower, or the system is Fedora 33 with any QEMU version
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Check for megasas-gen2 device usageInspect QEMU command-line arguments or VM configuration files (such as libvirt XML, VM start scripts, or cloud-init configs) for '-device megasas-gen2' or similar megasas device argumentsAffected if The megasas-gen2 SCSI adapter is configured or being emulated for a virtual machine
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Verify host kernel and firmwareCheck if the host is running a recent kernel and that any PCIe pass-through or hardware configuration is present for the megasas controllerAffected if The vulnerable code path in megasas_command_cancelled() can be triggered by a privileged guest with access to the megasas-gen2 emulated device
You are affected if QEMU version 6.0.0 or lower is installed AND a virtual machine is using the megasas-gen2 SCSI host bus adapter emulation, which allows a privileged guest user to crash the QEMU host process.
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 QEMU to a version beyond 6.0 that contains the security patch, or apply the specific patch for this vulnerability to the megasas_command_cancelled() function to add proper NULL pointer validation before dereferencing.
Fix this in Fedora
Scoped from the published advisory
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-35503 — 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-2020-35503 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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