CVE-2026-91191: Signature Bypass (CVSS 7.5)

Description

The device's update mechanism includes conditions that allow unauthorized software packages to be accepted as authentic. During the boot process, the stock done function disables signature verification in the OPKG configuration before restoring optional packages from a writable, unsigned feed. Separately, the publicly distributed SDK contains the production private key whose corresponding public key is trusted by both stable and beta firmware builds. Either issue undermines package authenticity, and together they allow an attacker to provide packages that appear valid to the system. Even if signature enforcement is restored, the exposed production key enables an attacker to generate signatures that the device will continue to trust. An attacker who can supply a malicious package may be able to execute arbitrary code with root privileges during installation.

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CVSS v3.1 Score

7.5

HIGH

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

EPSS — Exploit Prediction

0.0021

Probability of exploitation

0.10%

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-347 CWE-347

References

Other References

https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-272-01.json https://ltrxdev.atlassian.net/wiki/spaces/LTRXTS/pages/1889828865/Latest+firmware+for+the+G520+Series+G526+G526RP+G527+G528 https://www.cisa.gov/news-events/ics-advisories/icsa-26-272-01 https://www.lantronix.com/technical-support/security-updates/vulnerability-disclosure-policy/vulnerability-library/

Frequently Asked Questions

What is CVE-2026-91191? +

The device's update mechanism includes conditions that allow unauthorized software packages to be accepted as authentic. During the boot process, the stock done function disables signature verification in the OPKG configuration before restoring optional packages from a writable, unsigned feed. Separately, the publicly distributed SDK contains the production private key whose corresponding public key is trusted by both stable and beta firmware builds. Either issue undermines package authenticity, and together they allow an attacker to provide packages that appear valid to the system. Even if signature enforcement is restored, the exposed production key enables an attacker to generate signatures that the device will continue to trust. An attacker who can supply a malicious package may be able to execute arbitrary code with root privileges during installation. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-91191? +

CVE-2026-91191 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0021, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-91191? +

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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