CVE-2026-55490: openwrt Integer Underflow

Description

OpenWrt is a Linux operating system targeting embedded devices. Before v25.12.5, an integer underflow in handle_send_a() of the Emergency Access Daemon allows any unauthenticated attacker on the local network to crash the daemon by sending a single crafted UDP packet. The message length underflows before a bounds check and is then passed to memcpy as a very large size. This issue is fixed v25.12.5.

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CVSS v3.1 Score

6.5

MEDIUM

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

EPSS — Exploit Prediction

0.0068

Probability of exploitation

0.49%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-191 CWE-191

Affected Products

Vendor	Product	Versions
openwrt	openwrt	< 25.12.5

References

Advisories & Patches

https://github.com/openwrt/openwrt/commit/63c0767f3d02f7b10b0f0b5293366bd059a08ca5 https://github.com/openwrt/openwrt/security/advisories/GHSA-9558-77jp-g3fw

Exploits

https://github.com/openwrt/openwrt/security/advisories/GHSA-9558-77jp-g3fw

Other References

https://github.com/openwrt/openwrt/releases/tag/v25.12.5

Frequently Asked Questions

What is CVE-2026-55490? +

OpenWrt is a Linux operating system targeting embedded devices. Before v25.12.5, an integer underflow in handle_send_a() of the Emergency Access Daemon allows any unauthenticated attacker on the local network to crash the daemon by sending a single crafted UDP packet. The message length underflows before a bounds check and is then passed to memcpy as a very large size. This issue is fixed v25.12.5. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-55490? +

CVE-2026-55490 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0068, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-55490? +

CVE-2026-55490 affects products from openwrt, specifically: openwrt. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-55490? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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