CVE-2026-55490Public exploit

Pre-auth daemon crash via message-length underflow

Published Jul 7, 2026 · Updated Jul 7, 2026

Integer underflow in OpenWrt before 25.12.5 allows remote attackers on the local network to crash the Emergency Access Daemon. In handle_send_a(), a zero message length wraps to -1, bypasses the signed upper-bound check, and reaches memcpy as SIZE_MAX against a 257-byte buffer. Exposure requires EAD to be enabled and reachable on UDP port 56026; a valid local username is sufficient, and a successful packet interrupts emergency recovery access.

CVSS severity6.5
Medium
EPSS probability0.68%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer underflow in OpenWrt before 25.12.5 allows remote attackers on the local network to crash the Emergency Access Daemon. In handle_send_a(), a zero message length wraps to -1, bypasses the signed upper-bound check, and reaches memcpy as SIZE_MAX against a 257-byte buffer. Exposure requires EAD to be enabled and reachable on UDP port 56026; a valid local username is sufficient, and a successful packet interrupts emergency recovery access.

The record

CVE
CVE-2026-55490
Published
Jul 7, 2026
Updated
Jul 7, 2026
Vendor
OpenWrt
Product
OpenWrt
Classifications
CWE-191, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 25.12.5

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

OpenWrt · OpenWrtversion=< 25.12.5

Published CVSS scores

6.5GitHub, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-191Integer Underflow (Wrap or Wraparound)
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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