dbcve.org
OpenwrtOperating system

CVE-2026-30871

CRITICAL · 9.8 CVSS v3.1 Published 2026-03-19
Fix available
A fix is available. Upgrade to 24.10.6 / 25.12.1 or later.
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
OpenWrt Project is a Linux operating system targeting embedded devices. In versions prior to 24.10.6 and 25.12.1, the mdns daemon has a Stack-based Buffer Overflow vulnerability in the parse_question function. The issue is triggered by PTR queries for reverse DNS domains (.in-addr.arpa and .ip6.arpa). DNS packets received on UDP port 5353 are expanded by dn_expand into an 8096-byte global buffer (name_buffer), which is then copied via an unbounded strcpy into a fixed 256-byte stack buffer when handling TYPE_PTR queries. The overflow is possible because dn_expand converts non-printable ASCII bytes (e.g., 0x01) into multi-character octal representations (e.g., \001), significantly inflating the expanded name beyond the stack buffer's capacity. A crafted DNS packet can exploit this expansion behavior to overflow the stack buffer, making the vulnerability reachable through normal multicast DNS packet processing. This issue has been fixed in versions 24.10.6 and 25.12.1.

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

Stack-based Buffer Overflow in OpenWrt mdns daemon's parse_question function. When processing PTR queries for reverse DNS domains (.in-addr.arpa/.ip6.arpa), dn_expand expands DNS names into an 8096-byte global buffer, then copies via unbounded strcpy into a 256-byte stack buffer. Non-printable ASCII bytes are converted to multi-character octal representations (e.g., 0x01 becomes \001), inflating the expanded name beyond the 256-byte stack buffer capacity, allowing overflow via crafted mDNS packets on UDP port 5353.

MitigationUpgrade OpenWrt to version 24.10.6 or 25.12.1 or later. If upgrade not feasible, consider firewall rules to restrict mDNS traffic (UDP 5353) to trusted sources.

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
OpenwrtOperating system
Affected:< 24.10.6>= 25.12.0, < 25.12.1

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. Check OpenWrt version
    Run `cat /etc/os-release` or `cat /etc/openwrt_version` to see the installed OpenWrt version
    Affected if The version is less than 24.10.6, or greater than or equal to 25.12.0 but less than 25.12.1
  2. Verify mdns daemon is running
    Run `ps w | grep -i mdns` or check if the mdns service process is active
    Affected if The mdns or mdnsd daemon is running on the system
  3. Confirm mDNS service is enabled
    Check /etc/config/mdns for 'option enabled 1' or similar configuration indicating mDNS is enabled
    Affected if mDNS service is enabled in the configuration
  4. Inspect firewall rules for UDP port 5353
    Run `iptables -L -n | grep 5353` or examine /etc/config/firewall for mDNS traffic rules
    Affected if UDP port 5353 (mDNS) is accessible from untrusted network interfaces

A system is affected if it runs a vulnerable OpenWrt version (less than 24.10.6 or 25.12.0-25.12.1) with the mDNS daemon enabled and UDP port 5353 exposed to network traffic.

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 24.10.6 / 25.12.1 or later
Fixed in 24.10.625.12.1
Interim mitigation

Upgrade OpenWrt to version 24.10.6 or 25.12.1 or later. If upgrade not feasible, consider firewall rules to restrict mDNS traffic (UDP 5353) to trusted sources.

Recommended fix High confidence

Upgrade to OpenWrt 24.10.6 or 25.12.1 (whichever release branch you are using)

  1. 1. Identify the current OpenWrt version by running 'cat /etc/os-release' or 'luci > Status > Overview' in the web interface
  2. 2. Determine if the installed version is affected: versions < 24.10.6 or >= 25.12.0 but < 25.12.1 are vulnerable
  3. 3. Obtain the appropriate fixed firmware image (24.10.6 or 25.12.1) from the official OpenWrt downloads page based on your device architecture
  4. 4. Back up current configuration using 'sysupgrade -b /tmp/backup.tar.gz' or via LuCI System > Backup / Flash Firmware
  5. 5. Flash the fixed firmware using 'sysupgrade -v /path/to/openwrt-*-firmware.bin' or via LuCI web interface
  6. 6. After reboot, verify the new version is running: 'cat /etc/os-release' should show version 24.10.6 or 25.12.1
  7. 7. Restore configuration from backup if needed using 'sysupgrade -r /tmp/backup.tar.gz'
Caveat Standard firmware upgrade risks apply - review release notes for any configuration or package compatibility changes before upgrading

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

Fix this in Openwrt Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
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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-2026-30871 in production — separate from our analysis above.

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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