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FreeBSDOperating system

CVE-2020-25583

CRITICAL · 9.8 CVSS v3.1 Published 2021-03-29
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 · unedited
In FreeBSD 12.2-STABLE before r368250, 11.4-STABLE before r368253, 12.2-RELEASE before p1, 12.1-RELEASE before p11 and 11.4-RELEASE before p5 when processing a DNSSL option, rtsold(8) decodes domain name labels per an encoding specified in RFC 1035 in which the first octet of each label contains the label's length. rtsold(8) did not validate label lengths correctly and could overflow the destination buffer.

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 confidence

Buffer overflow vulnerability in FreeBSD's rtsold(8) daemon when processing the DNSSL (DNS Search List) option in router advertisements. The daemon decodes domain name labels per RFC 1035 encoding but fails to properly validate label lengths before copying into a fixed-size buffer, allowing potential remote code execution by adjacent network attackers.

MitigationApply FreeBSD security patches (r368250 for 12.2-STABLE, r368253 for 11.4-STABLE, or release patches p1/p11/p5) to add proper label length validation, or upgrade to patched FreeBSD versions.

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
FreeBSDOperating system
Affected:= 11.3= 11.4= 12.1= 12.2

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify FreeBSD version
    Run 'freebsd-version -k' or 'uname -r' to get the running kernel version
    Affected if The version matches 11.3, 11.4, 12.1, or 12.2
  2. Confirm rtsold daemon is enabled
    Check /etc/rc.conf for 'rtsold_enable="YES"' or run 'ps aux | grep rtsold' to see if the process is running
    Affected if rtsold is enabled and running as a daemon
  3. Verify IPv6 is configured
    Check if IPv6 is enabled via 'ifconfig -a' showing inet6 interfaces or sysctl net.inet6.ip6.accept_rtadv
    Affected if IPv6 is enabled and the system accepts router advertisements
  4. Confirm router advertisement processing
    Check sysctl net.inet6.icmp6.rtadv_accept or examine /etc/rc.conf for 'ipv6_enable="YES"' and ipv6_router_accept_variables
    Affected if The system is configured to process router advertisements, enabling DNSSL option processing by rtsold

You are affected if your FreeBSD version is 11.3, 11.4, 12.1, or 12.2 AND rtsold is running while the system accepts IPv6 router advertisements that include DNSSL options.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply FreeBSD security patches (r368250 for 12.2-STABLE, r368253 for 11.4-STABLE, or release patches p1/p11/p5) to add proper label length validation, or upgrade to patched FreeBSD versions.

Recommended fix High confidence

Upgrade to the respective patch level: 11.4-RELEASE-p5, 12.1-RELEASE-p11, 12.2-RELEASE-p1, or migrate to 12.4-STABLE/13.x for 11.3 users

  1. Identify your current FreeBSD version using 'freebsd-version' or 'uname -a'
  2. For FreeBSD 11.4: Upgrade to FreeBSD 11.4-RELEASE-p5 or later using 'freebsd-update fetch install'
  3. For FreeBSD 12.1: Upgrade to FreeBSD 12.1-RELEASE-p11 or later using 'freebsd-update fetch install'
  4. For FreeBSD 12.2: Upgrade to FreeBSD 12.2-RELEASE-p1 or later using 'freebsd-update fetch install'
  5. For FreeBSD 11.3: This version is End-of-Life; upgrade to a supported branch such as 12.4-STABLE or 13.x-STABLE
  6. After upgrade, verify rtsold version with 'rtsold -v' and confirm the patch is applied by checking the security advisory at security.FreeBSD.org
Caveat FreeBSD 11.3 is End-of-Life and no longer receives security patches; upgrading to 12.x or 13.x may require application compatibility testing

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in FreeBSD Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
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Scan for this in your stack

Free · runs locally
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-25583 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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