dbcve.org
FreeBSDOperating system

CVE-2020-25577

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 rtsold(8) does not verify that the RDNSS option does not extend past the end of the received packet before processing its contents. While the kernel currently ignores such malformed packets, it passes them to userspace programs. Any programs expecting the kernel to do validation may be vulnerable to an overflow.

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

In FreeBSD, the rtsold(8) daemon does not validate that the RDNSS option in router advertisement packets does not extend past the end of the received packet before processing. While the kernel ignores malformed packets, it passes them to userspace programs like rtsold that may expect kernel-level validation. This allows a malicious or crafted router advertisement to trigger an out-of-bounds read in rtsold, leading to potential memory disclosure or denial of service.

MitigationUpdate to FreeBSD patched versions: 12.2-STABLE r368250+, 11.4-STABLE r368253+, 12.2-RELEASE p1+, 12.1-RELEASE p11+, or 11.4-RELEASE p5+. If immediate patching is not possible, disable rtsold or restrict which network interfaces it monitors.

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:= 11.4= 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. Verify rtsold daemon is running
    Execute 'ps aux | grep rtsold' or 'pgrep rtsold' to see if the daemon process is active
    Affected if rtsold process is running - the vulnerability only applies when the daemon is active
  2. Check if rtsold is enabled at startup
    Review /etc/rc.conf for 'rtsold_enable=YES' or check /etc/rc.d/rtsold scripts
    Affected if rtsold is configured to start automatically at boot
  3. Determine FreeBSD version
    Run 'freebsd-version' or 'uname -r' to identify the installed FreeBSD release version
    Affected if Version is 11.4, 12.1, or 12.2 (or any variant of these releases)
  4. Check for patches in system logs
    Review /var/log/messages or output of 'zpool status' for recent patch-related updates mentioning r368250, r368253, or corresponding stable branches
    Affected if System has NOT been updated to patched versions (12.2-STABLE r368250+, 11.4-STABLE r368253+, 12.2-RELEASE p1+, 12.1-RELEASE p11+, or 11.4-RELEASE p5+)

System is affected if rtsold daemon is running on an unpatched FreeBSD 11.4, 12.1, or 12.2 installation.

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

Update to FreeBSD patched versions: 12.2-STABLE r368250+, 11.4-STABLE r368253+, 12.2-RELEASE p1+, 12.1-RELEASE p11+, or 11.4-RELEASE p5+. If immediate patching is not possible, disable rtsold or restrict which network interfaces it monitors.

Recommended fix High confidence

FreeBSD 12.2-RELEASE-p1+, 12.1-RELEASE-p11+, or 11.4-RELEASE-p5+ (or stable branches r368250+/r368253+)

  1. Backup critical data and configuration files before proceeding
  2. Update the FreeBSD package repository: pkg update
  3. For FreeBSD 12.2: Upgrade to version 12.2-RELEASE-p1 or later using: freebsd-update fetch install or reboot into the new kernel
  4. For FreeBSD 12.1: Upgrade to version 12.1-RELEASE-p11 or later using: freebsd-update fetch install or reboot into the new kernel
  5. For FreeBSD 11.4: Upgrade to version 11.4-RELEASE-p5 or later using: freebsd-update fetch install or reboot into the new kernel
  6. Alternatively, switch to a stable branch (e.g., 12.2-STABLE or 11.4-STABLE) with revisions after r368250 or r368253 respectively
  7. After reboot, verify the rtsold version is updated: rtsold -v
  8. Verify the fix by checking that rtsold no longer processes RDNSS options that extend beyond packet boundaries
Caveat Standard FreeBSD upgrade risks apply - review release notes for any configuration changes or deprecated features before upgrading production systems

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

Fix this in FreeBSD Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2020-25577 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