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FreeBSDOperating system

CVE-2026-4748

HIGH · 7.5 CVSS v3.1 Published 2026-04-01
Fix available
A fix is available. Upgrade to 14.4 or later.
See remediation →
84/100
Remediation priority · High
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
A regression in the way hashes were calculated caused rules containing the address range syntax (x.x.x.x - y.y.y.y) that only differ in the address range(s) involved to be silently dropped as duplicates. Only the first of such rules is actually loaded into pf. Ranges expressed using the address[/mask-bits] syntax were not affected. Some keywords representing actions taken on a packet-matching rule, such as 'log', 'return tll', or 'dnpipe', may suffer from the same issue. It is unlikely that users have such configurations, as these rules would always be redundant. Affected rules are silently ignored, which can lead to unexpected behaviour including over- and underblocking.

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

A regression in pf's hash calculation causes rules using address range syntax (x.x.x.x - y.y.y.y) to be incorrectly identified as duplicates when they differ only in the address range. Only the first rule is loaded while subsequent rules are silently dropped. Similar issues may affect rules with keywords like 'log', 'return ttl', or 'dnpipe'. This leads to unexpected over- or under-blocking as rules are missing from the firewall configuration.

MitigationAudit pf.conf for rules using address range syntax (x.x.x.x - y.y.y.y) and convert them to the address[/mask-bits] syntax which is not affected. Verify all expected rules are actually loaded using 'pfctl -sr' and test firewall behavior to confirm expected blocking is occurring.

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:>= 14.0, < 14.4= 14.3= 14.4= 15.0

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
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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. Check FreeBSD version
    Run 'uname -r' or 'freebsd-version -u' to get the exact FreeBSD version
    Affected if Version is 14.0, 14.1, 14.2, 14.3, 14.4, or 15.0 (the version falls within >= 14.0 and <= 15.0)
  2. Verify pf firewall is enabled
    Run 'pfctl -si' to check pf status or check for pf in the running kernel with 'kldstat | grep pf'
    Affected if pf is loaded and active
  3. Find address range syntax in pf.conf
    Search pf.conf (typically at /etc/pf.conf) for the pattern 'xxx.xxx.xxx.xxx - yyy.yyy.yyy.yyy' using grep with a regex like '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+[[:space:]]*-[[:space:]]*[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+'
    Affected if Any rules use the address range syntax (IP - IP) rather than CIDR notation
  4. Find rules with affected keywords
    Grep pf.conf for 'log', 'return ttl', or 'dnpipe' keywords that may also trigger the hash collision issue
    Affected if Rules contain any of these keywords in combination with address specifications
  5. Compare configured vs loaded rules
    Run 'pfctl -sr' to list all currently loaded rules, then manually compare the count and content against the rules defined in pf.conf
    Affected if The loaded ruleset is missing rules that exist in pf.conf, particularly rules using address range syntax or affected keywords

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
Upgrade available Upgrade to 14.4 or later
Fixed in 14.4
Interim mitigation

Audit pf.conf for rules using address range syntax (x.x.x.x - y.y.y.y) and convert them to the address[/mask-bits] syntax which is not affected. Verify all expected rules are actually loaded using 'pfctl -sr' and test firewall behavior to confirm expected blocking is occurring.

Recommended fix Moderate confidence

FreeBSD 14.4 or latest stable release (check security.freebsd.org for availability)

  1. Check current pf rules for any rules using the address range syntax (x.x.x.x - y.y.y.y) to identify potentially affected configurations
  2. Review pf.conf for any redundant-looking rules that might have been silently dropped due to this bug
  3. Before upgrading, backup the current pf.conf configuration
  4. Upgrade to FreeBSD 14.4 or later if available, or to the latest stable release that includes the security fix for this regression
  5. After upgrade, verify that all expected pf rules are loaded by comparing rule count and testing rule matching behavior
  6. Monitor network traffic to confirm expected filtering behavior is restored

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

Fix this in FreeBSD Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2026-4748 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