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Full vulnerability report · 2026
CVE-2026-7273High confidence

Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

Zyxel · GS1900 Series Switches

8.8HighCVSS 3.1
Recommended action
Protect now

CISA confirms exploitation in the wild and lists 2026-09-24 as the remediation due date.

Fix not verified
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 21 Sep 2026

Evidence used

  • CISA confirms exploitation in the wild.
  • A structured source references public exploit or proof-of-concept material.
  • EPSS is 2.73% for the current model date.

Compensating controls

  • Restrict local access and enforce least privilege on affected hosts.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Zyxel GS1900 Series Switches and falls inside the recorded affected range.
  2. Recheck the vendor advisory before scheduling a change because no verified fixed version is currently retained.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-37030

CISA KEV mirrored by ENISA

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.

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 21 Sep 2026. Evidence sources: cisa_kev.
ENISA score
8.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionProtect now

CISA confirms exploitation in the wild and lists 2026-09-24 as the remediation due date.

Fix not verified
01

What, why and how

Zyxel GS1900 series switches contain a stack-based buffer overflow vulnerability in the CGI program which could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.

What

Zyxel GS1900 series switches contain a stack-based buffer overflow vulnerability in the CGI program which could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.

Why

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

How

An attacker operating through an adjacent network may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Zyxel GS1900 series switches contain a stack-based buffer overflow vulnerability in the CGI program which could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.

Why

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

How

An attacker operating through an adjacent network may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2026-09-21.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
an adjacent network → Stack-based Buffer Overflow → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Adjacent
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-121 ↗

CWE-121: Stack-based Buffer Overflow. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVAdjacentAttack vector: The attacker must be on an adjacent or logically close network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
UnauthenticatedCWE-121CISA KEVPublic exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-37030Known-exploited evidence recorded

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.

Official EUVD record ↗
Canadian Centre for Cyber Security · English · AV26-603Zyxel security advisory (AV26-603) – Update 1

On June 16, 2026, Zyxel published a security advisory to address vulnerabilities in the following products: On September 21, 2026, Cybersecurity and Infrastructure Security Agency (CISA) added CVE-2026-7273 to their Known Exploited Vulnerabilities (KEV) Database.

Official advisory ↗
NBSZ-NKI · Hungarian · cve-2026-7273CVE-2026-7273

Olyan feltétel, amikor a felülírandó puffer a veremben van kiosztva (azaz egy helyi változó vagy ritkán egy függvény paramétere).

Official advisory ↗
CSIRT Italia · Italian · rilevata-vulnerabilita-in-prodotti-zyxel-1Rilevata vulnerabilità in prodotti Zyxel

Rilevata una nuova vulnerabilità con gravità “alta”, nei firmware degli switch Zyxel GS1900. Tale vulnerabilità, qualora sfruttata, potrebbe consentire ad un utente malintenzionato di inviare una richiesta HTTP malevola per eseguire codice arbitrario sui sistemi interessati.

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-6963美 CISA 발표 주요 Exploit 정보공유(Update. 2026-09-21)

Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix not verified
Affected
  • GS1900-48HPv2 firmware: <= 2.90(ABTQ.1)C0
  • GS1900-8 firmware: <= 2.90(AAHH.1)C0
  • GS1900-8HP firmware: <= 2.90(AAHI.1)C0
  • GS1900-10HP firmware: <= 2.90(AAZI.1)C0
  • GS1900-16 firmware: <= 2.90(AAHJ.1)C0
  • GS1900-24 firmware: <= 2.90(AAHL.1)C0
  • GS1900-24E firmware: <= 2.90(AAHK.1)C0
  • GS1900-24EP firmware: <= 2.90(ABTO.1)C0
  • GS1900-24HPv2 firmware: <= 2.90(ABTP.1)C0
  • GS1900-48 firmware: <= 2.90(AAHN.1)C0
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 16 Jun 2026 · Last source change 22 Sept 2026, 03:55 UTC · CWE-121 · Stack-based Buffer Overflow

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-37030
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. BlackTree coverageBlackTree article coverage changed from 1 BlackTree article to 1 BlackTree article.
    Before
    1 BlackTree article
    After
    1 BlackTree article
    BlackTree editorial ↗
  2. BlackTree coverageBlackTree article coverage changed from no BlackTree article to 1 BlackTree article.
    Before
    no BlackTree article
    After
    1 BlackTree article
    BlackTree editorial ↗
  3. ENISA known-exploited stateENISA EUVD now records this CVE in its known-exploited dataset.
    Before
    not listed in ENISA EUVD known-exploited dataset
    After
    listed in ENISA EUVD known-exploited dataset (EUVD-2026-37030)
    ENISA EUVD ↗
  4. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/zyxel-security-advisory-av26-603.
    Before
    remediation: cyber.gc.ca/zyxel-security-advisory-av26-603 · vendor advisory: zyxel.com/zyxel-security-advisory-for-stack-based-buffer-overflow-vulnerability-in-gs1900-series-switches-06-16-2026
    After
    vendor advisory: zyxel.com/zyxel-security-advisory-for-stack-based-buffer-overflow-vulnerability-in-gs1900-series-switches-06-16-2026
    security@zyxel.com.tw ↗
  5. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    security@zyxel.com.tw ↗
  6. Vendor guidanceAuthoritative vendor guidance changed: added vendor advisory: zyxel.com/zyxel-security-advisory-for-stack-based-buffer-overflow-vulnerability-in-gs1900-series-switches-06-16-2026.
    Before
    no authoritative guidance recorded
    After
    vendor advisory: zyxel.com/zyxel-security-advisory-for-stack-based-buffer-overflow-vulnerability-in-gs1900-series-switches-06-16-2026
    security@zyxel.com.tw ↗
  7. Public exploit evidencePublic exploit evidence changed from No public exploit to Public exploit reference.
    Before
    No public exploit
    After
    Public exploit reference
    greynoise.io ↗
  8. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/zyxel-security-advisory-av26-603.
    Before
    remediation: cyber.gc.ca/zyxel-security-advisory-av26-603
    After
    no authoritative guidance recorded
    CISA KEV ↗
  9. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    CISA KEV ↗
  10. Remediation statusRemediation status changed from Awaiting fix to Mitigation available.
    Before
    Awaiting fix
    After
    Mitigation available
    Canadian Centre for Cyber Security ↗
  11. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/zyxel-security-advisory-av26-603.
    Before
    remediation: cyber.gc.ca/zyxel-security-advisory-av26-603
    After
    no authoritative guidance recorded
    CISA KEV ↗
  12. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    CISA KEV ↗
  13. Affected versionsThe structured affected or fixed version information changed.
    Before
    <= 2.90(ABTQ.1)C0; <= 2.90(AAHH.1)C0; <= 2.90(AAHI.1)C0; <= 2.90(AAZI.1)C0; <= 2.90(AAHJ.1)C0; <= 2.90(AAHL.1)C0; <= 2.90(AAHK.1)C0; <= 2.90(ABTO.1)C0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    GS1900-48HPv2 firmware: <= 2.90(ABTQ.1)C0; GS1900-8 firmware: <= 2.90(AAHH.1)C0; GS1900-8HP firmware: <= 2.90(AAHI.1)C0; GS1900-10HP firmware: <= 2.90(AAZI.1)C0; GS1900-16 firmware: <= 2.90(AAHJ.1)C0; GS1900-24 firmware: <= 2.90(AAHL.1)C0; GS1900-24E firmware: <= 2.90(AAHK.1)C0; GS1900-24EP firmware: <= 2.90(ABTO.1)C0; GS1900-24HPv2 firmware: <= 2.90(ABTP.1)C0; GS1900-48 firmware: <= 2.90(AAHN.1)C0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CISA KEV ↗
  14. CISA KEV stateCISA KEV now confirms exploitation in the wild.
    Before
    not listed in CISA KEV
    After
    listed in CISA KEV since 2026-09-21
    CISA KEV ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
ENISA EUVD · EUVD-2026-37030↗CISA KEV record↗CVE authority or vendor reference↗Public exploit reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-7273 · cve.blacktree.nl