Debian LinuxOperating system · Debian
CVE-2024-8508
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 · uneditedNLnet Labs Unbound up to and including version 1.21.0 contains a vulnerability when handling replies with very large RRsets that it needs to perform name compression for. Malicious upstreams responses with very large RRsets can cause Unbound to spend a considerable time applying name compression to downstream replies. This can lead to degraded performance and eventually denial of service in well orchestrated attacks. The vulnerability can be exploited by a malicious actor querying Unbound for the specially crafted contents of a malicious zone with very large RRsets. Before Unbound replies to the query it will try to apply name compression which was an unbounded operation that could lock the CPU until the whole packet was complete. Unbound version 1.21.1 introduces a hard limit on the number of name compression calculations it is willing to do per packet. Packets that need more compression will result in semi-compressed packets or truncated packets, even on TCP for huge messages, to avoid locking the CPU for long. This change should not affect normal DNS traffic.
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 confidenceUnbound DNS resolver versions up to 1.21.0 contain an unbounded name compression algorithm vulnerability. When processing upstream responses containing very large resource record sets (RRsets), Unbound attempts to compress domain names without any computational limits. A malicious actor can exploit this by querying for specially crafted zones with extremely large RRsets, causing the name compression routine to consume excessive CPU time and potentially lock the processor until packet processing completes, leading to denial of service.
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
Debian LinuxOperating system
= 11.0< 1.21.1CVSS 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
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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 Unbound versionRun 'unbound -V' or check package manager output (dpkg -l unbound or rpm -qi unbound)Affected if Version is below 1.21.1 (any version from initial release up to 1.21.0)
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Confirm Unbound service is activeCheck process status: 'systemctl status unbound' or 'ps aux | grep unbound'Affected if Unbound daemon is running as a recursive resolver
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Verify recursive resolution is enabledReview /etc/unbound/unbound.conf for 'resolver' or 'recursive' configuration, and ensure 'do-not-query-localhost' is not set to disable recursionAffected if Unbound is configured as a recursive resolver (the default behavior) processing queries from network clients
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Check network exposureReview unbound.conf for 'interface:' directives and 'access-control:' settings to determine if the resolver accepts external queriesAffected if Unbound is accessible from network (not bound to localhost only with limited ACLs)
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Confirm upstream response processingVerify that the resolver is configured to fetch zone data from upstream nameservers (check for 'forward-zone:' with upstream addresses or default root hints)Affected if Unbound fetches and processes responses from upstream resolvers (required for the vulnerability to be triggered)
User is affected if running Unbound version below 1.21.1 as an externally accessible recursive DNS resolver that processes queries and fetches zone data from upstream servers.
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 · scoped1.21.1
Upgrade Unbound to version 1.21.1 or later, which implements a hard limit on name compression calculations per packet to prevent CPU exhaustion.
Unbound 1.21.1
- 1. Check the current Unbound version: `unbound -V` or `unbound-control status`
- 2. For Debian 11 (Bullseye), update package lists: `sudo apt update`
- 3. Upgrade Unbound to version 1.21.1 or later: `sudo apt install unbound=1.21.1-*` or `sudo apt install unbound` to get latest available
- 4. Verify the upgrade was successful: `unbound -V` and confirm version is 1.21.1 or higher
- 5. Restart the Unbound service: `sudo systemctl restart unbound`
- 6. Verify service is running properly: `sudo systemctl status unbound` or `unbound-control status`
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Debian Linux
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 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 $2,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2024-8508 — 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-2024-8508 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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