What is CVE-2026-7273?

CVE-2026-7273 is Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability. The supplied enrichment data classifies it as Memory Corruption mapped to CWE-121 Stack-based Buffer Overflow.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Yes: CISA KEV signal present. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

Is there a public exploit?

6 public PoC repositories reported; 0 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with Not reported where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-7273 using CVSS 8.8, EPSS 3%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Treat as emergency remediation because CISA KEV status is present. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

CISA KEVhighMemory Corruptionpublic exploit

CVE-2026-7273

CVE-2026-7273 — Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

Q: Is it in CISA KEV?

Yes. The supplied enrichment data lists CVE-2026-7273 in CISA KEV with required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

A stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions through 2.90(ABTQ.1)C0 could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.

Published Jun 16, 2026Updated Sep 21, 2026Sources: NVD, Zyxel (CNA), CISA, FIRST EPSS, GitHub, SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Confirmed

CISA KEV, listed Sep 21, 2026

EPSS

ahead of 84% of scored CVEs

Affects

Zyxel

10 products listed

CVSS base

8.8

high

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

Active

none · proof-of-concept · active

Automatable

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade GS1900-48HPv2 firmware to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

CISA required action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Federal deadline Sep 24, 2026 — passed 6 days ago

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Treat as emergency remediation because CISA KEV status is present.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
Zyxel	GS1900-48HPv2 firmware	<= 2.90(ABTQ.1)C0	Vulnerable
Zyxel	GS1900-8 firmware	<= 2.90(AAHH.1)C0	Vulnerable
Zyxel	GS1900-8HP firmware	<= 2.90(AAHI.1)C0	Vulnerable
Zyxel	GS1900-10HP firmware	<= 2.90(AAZI.1)C0	Vulnerable
Zyxel	GS1900-16 firmware	<= 2.90(AAHJ.1)C0	Vulnerable
Zyxel	GS1900-24 firmware	<= 2.90(AAHL.1)C0	Vulnerable
Zyxel	GS1900-24E firmware	<= 2.90(AAHK.1)C0	Vulnerable
Zyxel	GS1900-24EP firmware	<= 2.90(ABTO.1)C0	Vulnerable
Zyxel	GS1900-24HPv2 firmware	<= 2.90(ABTP.1)C0	Vulnerable
Zyxel	GS1900-48 firmware	<= 2.90(AAHN.1)C0	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Availability

High

Confidentiality

High

Integrity

High

Scope

Unchanged

Attack Complexity

Low

Attack Vector

Adjacent

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
8.8	CVSS 3.1	high	2.8	5.9	zyxel.com.tw (CNA), Zyxel (CNA)

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

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-121 · Stack-based Buffer Overflow

Modify Memory
DoS: Crash, Exit, or Restart
DoS: Resource Consumption (CPU)
DoS: Resource Consumption (Memory)

Mitigation: Run or compile the software using features or extensions that automatically provide a protection mechanism that mitigates or eliminates buffer overflows. For example, certain compilers and extensions provide automatic buffer overflow detection mechanisms that are built into the compiled code. Examples include the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice.

Weakness & attack patterns

CWE-121Stack-based Buffer Overflow

Inferred from the weakness class — not observed against this CVE.

CAPEC-100 · Overflow BuffersCAPEC-123 · Buffer Manipulation

CISA KEV details

CISA lists a CVE here once it has evidence of exploitation against real targets.

CISAThat month →

Listed

Sep 21, 2026

Federal deadline

Sep 24, 2026

passed 6 days ago

Ransomware use

Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a date to argue against.

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

Social mentions

Posts naming this CVE. Attention, not evidence of exploitation — it spikes on disclosure and decays whether or not anything is exploited.

1 more posts on this CVEShowing 5 of 6 · Who is discussing this CVE, and how loudlyUnlock free

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Monitor for scanner or exploit-pattern traffic after 6 public PoC repositories were reported.

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added to CISA KEV catalog
Sep 21, 2026 · CISA
Added · CVSS 3.1 8.8 (AV:A)
Sep 21, 2026 · NVD
Initial · CVE published
Jun 16, 2026 · NVD

Source activity

Readings a source repeats on a schedule, counted rather than listed.

4×TweetsJun 16, 2026 – Jun 25, 2026 · SOCRadar CTI
3×SvrsJun 18, 2026 – Jun 27, 2026 · SOCRadar CTI
2×CVE modified by MITRE: CVSS metrics updated.Jun 16, 2026 · SOCRadar CTI

References

6 on the record

www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-stack-based-buffer-overflow-vulnerability-in-gs1900-series-switches-06-16-2026
Vendor Advisory, NIST
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-7273
US Government Resource
www.greynoise.io/blog/open-season-on-kapibala-attacker-steals-government-records-wordpress-exploitation
Vendor Advisory
www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
US Government Resource
www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
US Government Resource
nvd.nist.gov/vuln/detail/CVE-2026-7273
Vendor Advisory

Coverage

2 stories from the feeds we poll

Elsewhere on this site

Zyxelevery CVE for this vendor
September 2026what else CISA listed
Memory Corruptionsame class
CWE-121other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-7273 is Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability, a high vulnerability affecting GS1900-48HPv2 firmware, GS1900-8 firmware, GS1900-8HP firmware, GS1900-10HP firmware, GS1900-16 firmware, GS1900-24 firmware, GS1900-24E firmware, GS1900-24EP firmware, GS1900-24HPv2 firmware, GS1900-48 firmware from Zyxel. The current evidence lists it in CISA KEV, and the exploit status is: Yes: CISA KEV signal present. Public exploit evidence is: 6 public PoC repositories reported; 0 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 8.8 describes technical severity, while EPSS 3% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.