CVE-2026-20276 / Cisco CISCO-SA-HARDENING-IOSXR-QG64NCM: Cisco IOS XR Software Security Hardening Release: September 2026

Recommended actionPatch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 260 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product

What, why and how

As part of Cisco's ongoing commitment to proactive security and product quality, the Cisco IOS XR Software engineering team has conducted a comprehensive internal security review. This review resulted in a software hardening releases that address multiple internally discovered vulnerabilities. The vulnerabilities tracked by CVE-2026-20276 are related to insufficient control flow management issues that are grouped under the Common Weakness Enumeration (CWE) CWE-691.

What

Why

The code does not sufficiently manage its control flow during execution, creating conditions in which the control flow can be modified in unexpected ways.

How

An attacker operating through a network path 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

Why

The code does not sufficiently manage its control flow during execution, creating conditions in which the control flow can be modified in unexpected ways.

How

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.

No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material

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

None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path: a network path → Insufficient Control Flow Management → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface: Network
Privileges required: None: unauthenticated exploitation is possible
User interaction: None
Attack complexity: Low: no specialised conditions are recorded
Security boundary: Changed: exploitation can affect a different security authority
Weakness ? CWE means Common Weakness Enumeration: a standard category for the underlying weakness.: CWE-691 ↗
CWE-691: Insufficient Control Flow Management. The code does not sufficiently manage its control flow during execution, creating conditions in which the control flow can be modified in unexpected ways.
CVSS vector ? CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a 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.SChangedScope: The attack can affect a component governed by a different security authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.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.

NetworkUnauthenticatedCWE-691

Official authority intelligence

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

ENISA EUVD · EUVD-2026-70203Official EUVD mapping

Official EUVD record ↗

BSI · German · WID-SEC-2026-3155Cisco IOS XR: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Cisco IOS XR ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗

Cyber Security Agency of Singapore · English · CSA-SB-20260909Security Bulletin 9 Sep 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 9 Sep 2026, published on 9 September 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗

INCIBE-CERT · Spanish · multiples-vulnerabilidades-en-productos-de-cisco-13Múltiples vulnerabilidades en productos de Cisco

Cisco ha publicado 7 vulnerabilidades: 2 de severidad crítica y 5 de severidad alta que, en caso de ser explotadas, podrían permitir a un atacante realizar una ejecución de código, una denegación de servicio o acceder a funciones o recursos protegidos sin autorización.

Official advisory ↗

CERT-FR · French · CERTFR-2026-AVI-1110Multiples vulnérabilités dans les produits Cisco

De multiples vulnérabilités ont été découvertes dans les produits Cisco. Certaines d'entre elles permettent à un attaquant de provoquer une exécution de code arbitraire à distance, un déni de service à distance et un contournement de la politique de sécurité.

Official advisory ↗

CSIRT Italia · Italian · risolte-vulnerabilita-in-prodotti-cisco-31Risolte vulnerabilità in prodotti Cisco

Cisco ha rilasciato aggiornamenti di sicurezza che risolvono 9 vulnerabilità, di cui 3 con gravità "critica" e 6 con gravità “alta”, che interessano diversi prodotti.

Official advisory ↗

KISA KrCERT/CC · Korean · KNVD-6943Cisco 제품 보안 업데이트 권고

Cisco IOS XR Software에서 발생하는 Insufficient Control Flow Management 취약점(CVE-2026-20276) [1][6]

Official advisory ↗

NCSC-NL · Dutch · NCSC-2026-0338Kwetsbaarheden verholpen in Cisco Nexus 9000 Series, IOS XR Software en Secure Email

Cisco's IOS XR Software team conducted an internal security review resulting in software hardening releases that address multiple vulnerabilities related to insufficient control flow management (CVE-2026-20276, CWE-691).

Official advisory ↗

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 availability varies by product
Affected: 3.9.0
3.9.1
3.8.2
3.8.3
3.8.4
3.9.2
Base
4.0.1
4.0.2
4.0.0
4.1.0
4.2.0
4.1.1
4.1.2
4.0.3
4.0.4
4.0.11
4.2.1
4.2.2
4.3.0
4.2.3
4.2.4
4.3.1
4.3.2
3.9.3
5.1.0
5.1.1
4.3.3
4.3.4
5.1.2
and 230 more
Fixed: No fixed version is explicitly recorded in the structured CVE data.
Action: Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround: No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.

Official vendor articles1 stored document

Linked articles are downloaded and versioned as source evidence. A CVE mention or approved update relationship does not, by itself, verify a fix for every product branch.

Cisco IOS XR Software Security Hardening Release: September 2026 →Original publisher ↗Searchable text snapshot · Captured 26 Sep 2026Home / Cisco Security / Security Advisories Cisco Security Advisory Cisco IOS XR Software Security Hardening Release: September 2026 Cisco IOS XR Software Security Hardening Release: September 2026 --> Cisco Security Advisory Cisco IOS XR Software Security Hardening Release: September 2026 Critical Advisory ID: ci

Evidence and provenance

Published 2 Sept 2026 · Last source change 18 Sept 2026, 12:10 UTC · CWE-691 · Insufficient Control Flow Management

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 2026-09-03

European sourceENISA EUVD · EUVD-2026-70203

Product sourceVendor CSAF · Cisco PSIRT

Remediation sourceVendor CSAF · Cisco PSIRT

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 ↗

18 Sep 2026, 12:10 UTC
Affected versionsThe structured affected or fixed version information changed.
Before
Cisco IOS XR Software: 6.5.29, 7.0.1, 6.5.26, 6.5.25, 6.5.28, 6.5.90, 7.1.1, 7.0.90, 6.7.1, 7.0.2, 7.1.15, 7.2.1, 7.1.2, 6.7.2, 7.0.11, 7.0.12, 7.0.14, 7.1.25, 7.2.12, 7.3.1, 7.1.3, 6.7.3, 7.4.1, 7.2.2, 6.7.4, 6.5.31, 7.3.15, 7.3.16, 6.8.1, 7.4.15, 6.5.32, 7.3.2, 7.5.1, 7.4.16, 7.3.27, 7.6.1, 7.5.2, 7.8.1, 7.6.15, 7.5.12, 7.8.12, 7.3.3, 7.7.1, 6.8.2, 7.3.4, 7.4.2, 6.7.35, 6.9.1, 7.6.2, 7.5.3, 7.7.2, 6.9.2, 7.9.1, 7.10.1, 7.8.2, 7.5.4, 6.5.33, 7.8.22, 7.7.21, 7.9.2, 7.3.5, 7.5.5, 7.11.1, 7.9.21, 7.10.2, 24.1.1, 7.6.3, 7.3.6, 7.5.52, 7.11.2, 24.2.1, 24.1.2, 24.2.11, 24.3.1, 24.4.1, 24.2.2, 7.8.23, 7.11.21, 24.2.20, 24.3.2, 24.4.10, 6.5.35, 25.1.1, 24.4.2, 24.3.20, 24.4.15, 25.2.1, 6.5.351, 25.1.2, 24.3.30, 25.3.1, 6.5.352, 24.4.30, 24.2.21, 25.4.1, 25.2.2, 25.2.15, 7.2.0, 7.0.0, 25.2.30, 6.5.353, 26.1.1, 25.1.30, 25.3.15, 26.2.100, 25.4.2, 26.2.1, 25.4.30, 26.1.2, 25.4.201, 26.2.101 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
After
Cisco IOS XR Software: 6.5.29, 7.0.1, 6.5.26, 6.5.25, 6.5.28, 6.5.90, 7.1.1, 7.0.90, 6.7.1, 7.0.2, 7.1.15, 7.2.1, 7.1.2, 6.7.2, 7.0.11, 7.0.12, 7.0.14, 7.1.25, 7.2.12, 7.3.1, 7.1.3, 6.7.3, 7.4.1, 7.2.2, 6.7.4, 6.5.31, 7.3.15, 7.3.16, 6.8.1, 7.4.15, 6.5.32, 7.3.2, 7.5.1, 7.4.16, 7.3.27, 7.6.1, 7.5.2, 7.8.1, 7.6.15, 7.5.12, 7.8.12, 7.3.3, 7.7.1, 6.8.2, 7.3.4, 7.4.2, 6.7.35, 6.9.1, 7.6.2, 7.5.3, 7.7.2, 6.9.2, 7.9.1, 7.10.1, 7.8.2, 7.5.4, 6.5.33, 7.8.22, 7.7.21, 7.9.2, 7.3.5, 7.5.5, 7.11.1, 7.9.21, 7.10.2, 24.1.1, 7.6.3, 7.3.6, 7.5.52, 7.11.2, 24.2.1, 24.1.2, 24.2.11, 24.3.1, 24.4.1, 24.2.2, 7.8.23, 7.11.21, 24.2.20, 24.3.2, 24.4.10, 6.5.35, 25.1.1, 24.4.2, 24.3.20, 24.4.15, 25.2.1, 6.5.351, 25.1.2, 24.3.30, 25.3.1, 6.5.352, 24.4.30, 24.2.21, 25.4.1, 25.2.2, 25.2.15, 7.2.0, 7.0.0, 25.2.30, 6.5.353, 26.1.1, 25.1.30, 25.3.15, 26.2.100, 25.4.2, 26.2.1, 25.4.30, 26.1.2, 25.4.201, 26.2.101, 25.2.21 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
CNA ↗
17 Sep 2026, 21:13 UTC
Remediation statusRemediation status changed from Awaiting fix to Mitigation available.
Before
Awaiting fix
After
Mitigation available
Cisco PSIRT ↗
16 Sep 2026, 03:56 UTC
Vendor guidanceAuthoritative vendor guidance changed: added vendor advisory: sec.cloudapps.cisco.com/cisco-sa-hardening-iosxr-qg64NcM.
Before
no authoritative guidance recorded
After
vendor advisory: sec.cloudapps.cisco.com/cisco-sa-hardening-iosxr-qg64NcM
psirt@cisco.com ↗
15 Sep 2026, 17:03 UTC
Affected versionsThe structured affected or fixed version information changed.
Before
6.5.29; 7.0.1; 6.5.26; 6.5.25; 6.5.28; 6.5.90; 7.1.1; 7.0.90 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
After
Cisco IOS XR Software: 6.5.29, 7.0.1, 6.5.26, 6.5.25, 6.5.28, 6.5.90, 7.1.1, 7.0.90, 6.7.1, 7.0.2, 7.1.15, 7.2.1, 7.1.2, 6.7.2, 7.0.11, 7.0.12, 7.0.14, 7.1.25, 7.2.12, 7.3.1, 7.1.3, 6.7.3, 7.4.1, 7.2.2, 6.7.4, 6.5.31, 7.3.15, 7.3.16, 6.8.1, 7.4.15, 6.5.32, 7.3.2, 7.5.1, 7.4.16, 7.3.27, 7.6.1, 7.5.2, 7.8.1, 7.6.15, 7.5.12, 7.8.12, 7.3.3, 7.7.1, 6.8.2, 7.3.4, 7.4.2, 6.7.35, 6.9.1, 7.6.2, 7.5.3, 7.7.2, 6.9.2, 7.9.1, 7.10.1, 7.8.2, 7.5.4, 6.5.33, 7.8.22, 7.7.21, 7.9.2, 7.3.5, 7.5.5, 7.11.1, 7.9.21, 7.10.2, 24.1.1, 7.6.3, 7.3.6, 7.5.52, 7.11.2, 24.2.1, 24.1.2, 24.2.11, 24.3.1, 24.4.1, 24.2.2, 7.8.23, 7.11.21, 24.2.20, 24.3.2, 24.4.10, 6.5.35, 25.1.1, 24.4.2, 24.3.20, 24.4.15, 25.2.1, 6.5.351, 25.1.2, 24.3.30, 25.3.1, 6.5.352, 24.4.30, 24.2.21, 25.4.1, 25.2.2, 25.2.15, 7.2.0, 7.0.0, 25.2.30, 6.5.353, 26.1.1, 25.1.30, 25.3.15, 26.2.100, 25.4.2, 26.2.1, 25.4.30, 26.1.2, 25.4.201, 26.2.101 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
CNA ↗
3 Sep 2026, 15:38 UTC
BlackTree coverageBlackTree article coverage changed from no BlackTree article to 1 BlackTree article.
Before
no BlackTree article
After
1 BlackTree article
BlackTree editorial ↗
2 Sep 2026, 20:03 UTC
ENISA EUVD mappingEUVD-2026-70203 was added to the official ENISA EUVD mapping for this CVE.
Before
not recorded
After
{"euvdId":"EUVD-2026-70203"}
ENISA EUVD ↗
2 Sep 2026, 16:13 UTC
Catalogue recordCVE added to the BlackTree catalogue.
CNA ↗

2026-09-02CVE published

2026-09-17Remediation guidance recorded

ENISA EUVD · EUVD-2026-70203↗CVE authority or vendor reference · Cisco CISCO-SA-HARDENING-IOSXR-QG64NCM↗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.

Cisco IOS XR Software Security Hardening Release: September 2026

Published severity in operational context

Evidence used

Compensating controls

Verification

Remediation availability differs by product scope

Authoritative vendor CSAF and VEX advisories

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

ENISA European Vulnerability Database

EUVD-2026-70203

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

What changed after publication