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Stack-based Buffer OverflowWeakness · CWE-121

CVE-2025-11678

HIGH · 7.5 CVSS v4.0 Published 2025-10-20
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
78/100
Remediation priority · High
No privileges

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
Stack-based Buffer Overflow in lws_adns_parse_label in warmcat libwebsockets allows, when the LWS_WITH_SYS_ASYNC_DNS flag is enabled during compilation, to overflow the label_stack, when the attacker is able to sniff a DNS request in order to craft a response with a matching id containing a label longer than the maximum.

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 · moderate confidence

A stack-based buffer overflow exists in libwebsockets' async DNS parsing function lws_adns_parse_label. When the LWS_WITH_SYS_ASYNC_DNS build flag is enabled, the function fails to validate the length of DNS label fields before copying them into a fixed-size stack buffer (label_stack). An attacker who can sniff DNS traffic on the network can craft a malicious DNS response with a matching query ID containing a label exceeding the maximum allowed length, causing overflow.

MitigationDisable the LWS_WITH_SYS_ASYNC_DNS feature if not required, or apply a bounds-checking patch to lws_adns_parse_label that validates label lengths against the label_stack buffer size before copying.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
Adjacent
Complexity
Low
Privileges
None
Authentication
X
User interaction
P
Scope
X

CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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 libwebsockets installation and version
    Run 'pkg-config --modversion libwebsockets' or check the library file with 'ldd' and 'strings' to find the version string, or check build documentation for the version compiled into your application
    Affected if The installed version is within the affected range and you cannot determine if it was built without the vulnerable flag
  2. Verify build configuration for LWS_WITH_SYS_ASYNC_DNS
    Check your build system (CMake, Makefile, or build logs) for the CMake flag '-DLWS_WITH_SYS_ASYNC_DNS=ON' or the preprocessor define 'LWS_WITH_SYS_ASYNC_DNS'. For compiled binaries, use 'strings <binary> | grep -i async_dns' or check for symbols related to 'lws_adns_parse_label'
    Affected if The library or application was built with LWS_WITH_SYS_ASYNC_DNS enabled (flag is ON or defined)
  3. Inspect the async DNS code path in the binary
    Use 'nm -gC <binary> | grep lws_adns_parse_label' to confirm the vulnerable function is present and linked, then check if the binary performs DNS lookups using libwebsockets async DNS functions
    Affected if The vulnerable function lws_adns_parse_label is present and the application uses async DNS resolution
  4. Confirm network exposure to DNS traffic
    Review network configuration and application logs to determine if DNS queries are being handled by libwebsockets and if the network path between DNS server and the application is sniffable by attackers
    Affected if The application processes DNS responses through libwebsockets on a network where DNS traffic can be intercepted

You are affected if your libwebsockets version contains the vulnerability, was built with LWS_WITH_SYS_ASYNC_DNS enabled, and processes DNS responses from a network path an attacker could sniff.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Disable the LWS_WITH_SYS_ASYNC_DNS feature if not required, or apply a bounds-checking patch to lws_adns_parse_label that validates label lengths against the label_stack buffer size before copying.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
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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-2025-11678 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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