VulnerabilityPublished 11 Sep 2026Updated 5 Oct 2026

CVE-2026-89726: Linux kernel · lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

Affects Linux kernelSource GCVE Database

Not known to be exploited.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 7% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Ubuntu 26.04 LTSlinux`pkg:deb/ubuntu/linux?arch=source&distro=resolute`Other threats	Affected 6.17.0-5.5 – 7.0.0-38.38 23 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-aws`pkg:deb/ubuntu/linux-aws?arch=source&distro=resolute`Other threats	Affected 6.17.0-1002.2 – 7.0.0-1014.14 15 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-azure`pkg:deb/ubuntu/linux-azure?arch=source&distro=resolute`Other threats	Affected 6.17.0-1003.3 – 7.0.0-1017.17 15 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-azure-fde`pkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resolute`Other threats	Affected 7.0.0-1003.3 – 7.0.0-1016.16 9 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-gcp`pkg:deb/ubuntu/linux-gcp?arch=source&distro=resolute`Other threats	Affected 6.17.0-1002.2 – 7.0.0-1014.14 13 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-gke`pkg:deb/ubuntu/linux-gke?arch=source&distro=resolute`Other threats	Affected 7.0.0-1002.3 – 7.0.0-1008.9 6 affected builds	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch fixing the off-by-one out-of-bounds read in ucs2_strnlen() has been released. Users and administrators should apply the official Linux kernel updates that include this fix for the affected versions. Since this is a code-level fix, upgrading to a patched kernel version is the recommended remediation. No additional mitigations are indicated by the vendor advisory.

Description

A medium severity vulnerability in the Linux kernel's lib/ucs2_string.c component was fixed to address an off-by-one out-of-bounds read in the ucs2_strnlen() function. The flaw occurs because the function checks the current character before verifying if the maximum length has been reached, potentially reading one ucs2_char_t past the intended boundary if the input is not NUL-terminated within the limit. This issue has been resolved by adjusting the length check to prevent the out-of-bounds read.

Impact

This vulnerability could cause an out-of-bounds read in kernel memory when processing certain UCS2 strings, potentially leading to information disclosure or kernel instability. However, no known exploits in the wild have been reported. The impact is considered medium severity due to the nature of the out-of-bounds read without confirmed active exploitation or direct code execution.

Summary

The Linux kernel contained an off-by-one out-of-bounds read vulnerability in the ucs2_strnlen() function located in lib/ucs2_string.c. The function previously checked the current character before confirming that the caller-provided maximum length was not exceeded, which could lead to reading one ucs2_char_t beyond the buffer if the input was not properly NUL-terminated within the specified bound. A patch series was released that fixes this by testing the length before dereferencing the character, preventing the out-of-bounds read. The patch also included a secondary fix for code indentation. Multiple specific Linux kernel versions are affected.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Oct 2026, 03:27 UTC

Technical details

References

Community reviews

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