BlackTreeCVE Intelligence
← Back to the CVE catalogue
Full vulnerability report · 2026
CVE-2026-20125High confidence

Cisco IOS — Improper Handling of Syntactically Invalid Structure

Cisco · IOS

Official source article: Cisco CISCO-SA-IOS-HTTP-DOS-SBV8XRPL ↗. Check the applicable product and release in the original source.

7.7HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Fix not verified
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.28% for the current model date.

Compensating controls

  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Cisco IOS 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 30 daysRemediation target: Within 180 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-2026-15449

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Fix not verified
01

What, why and how

A vulnerability in the HTTP Server feature of Cisco IOS Software and Cisco IOS XE Software Release 3E could allow an authenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper validation of user-supplied input. An attacker could exploit this vulnerability by sending malformed HTTP requests to an affected device. A successful exploit could allow the attacker to cause a watchdog timer to expire and the device to reload, resulting in a DoS condition. To exploit this vulnerability, the attacker must have a valid user account.

What

A vulnerability in the HTTP Server feature of Cisco IOS Software and Cisco IOS XE Software Release 3E could allow an authenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper validation of user-supplied input. An attacker could exploit this vulnerability by sending malformed HTTP requests to an affected device. A successful exploit could allow the attacker to cause a watchdog timer to expire and the device to reload, resulting in a DoS condition. To exploit this vulnerability, the attacker must have a valid user account.

Why

The product does not handle or incorrectly handles input that is not syntactically well-formed with respect to the associated specification.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

What

A vulnerability in the HTTP Server feature of Cisco IOS Software and Cisco IOS XE Software Release 3E could allow an authenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper validation of user-supplied input. An attacker could exploit this vulnerability by sending malformed HTTP requests to an affected device. A successful exploit could allow the attacker to cause a watchdog timer to expire and the device to reload, resulting in a DoS condition. To exploit this vulnerability, the attacker must have a valid user account.

Why

The product does not handle or incorrectly handles input that is not syntactically well-formed with respect to the associated specification.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

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.
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 → Improper Handling of Syntactically Invalid Structure → disrupt the affected service
Attack surface
Network
Privileges required
Low: a basic authenticated account is required
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-228 ↗

CWE-228: Improper Handling of Syntactically Invalid Structure. The product does not handle or incorrectly handles input that is not syntactically well-formed with respect to the associated specification.

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:L/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.PRLowPrivileges required: The attacker needs basic user-level 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.
NetworkDenial of serviceCWE-228
A

Official authority intelligence

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

BSI · German · WID-SEC-2026-0874Cisco IOS und IOS XE Software: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Cisco IOS XE, Cisco IOS und Cisco Catalyst ausnutzen, um sich erweiterte Rechte zu verschaffen, beliebigen Code auszuführen, Sicherheitsmaßnahmen zu umgehen, Cross-Site-Scripting-Angriffe durchzuführen, Daten zu manipulieren, vertrauliche Informationen offenzulegen und einen Denial-of-Service-Zustand herbeizuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260401Security Bulletin 01 Apr 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 01 Apr 2026, published on 1 April 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0361Multiples vulnérabilités dans Cisco IOS et IOS XE

De multiples vulnérabilités ont été découvertes dans Cisco IOS et IOS XE. Elles permettent à un attaquant de provoquer un déni de service à distance et un contournement de la politique de sécurité.

Official advisory ↗
NCSC-NL · Dutch · NCSC-2026-0104Kwetsbaarheden verholpen in Cisco IOS XE Software

An authenticated remote attacker can exploit a vulnerability in the HTTP Server feature of Cisco IOS and IOS XE Software Release 3E by sending malformed HTTP requests, causing an unexpected device reload and denial of service.

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
  • IOS: 12.2(33)CY, 12.2(33)CY1, 12.2(33)CY2, 12.2(55)SE, 12.2(55)SE3, 12.2(55)SE2, 12.2(58)SE, 12.2(55)SE1, 12.2(58)SE1, 12.2(55)SE4, 12.2(58)SE2, 12.2(55)SE5, 12.2(55)SE6, 12.2(55)SE7, 12.2(55)SE8, 12.2(55)SE9, 12.2(55)SE10, 12.2(55)SE11, 12.2(55)SE12, 12.2(55)SE13, 12.2(25)EZ, 12.2(25)EZ1, 12.2(58)EZ, 12.2(53)EZ, 12.2(55)EZ, 12.2(60)EZ, 12.2(60)EZ1, 12.2(60)EZ2, 12.2(60)EZ3, 12.2(60)EZ4, 12.2(60)EZ5, 12.2(60)EZ6, 12.2(60)EZ7, 12.2(60)EZ8, 12.2(60)EZ9, 12.2(60)EZ10, 12.2(60)EZ11, 12.2(60)EZ12, 12.2(60)EZ13, 12.2(60)EZ14, 12.2(60)EZ15, 12.2(33)SXI2, 12.2(33)SXI3, 12.2(33)SXI5, 12.2(33)SXI4a, 12.2(33)SXI4, 12.2(33)SXI2a, 12.2(33)SXI, 12.2(33)SXI6, 12.2(33)SXI7, 12.2(33)SXI1, 12.2(33)SXI8, 12.2(33)SXI9, 12.2(33)SXI8a, 12.2(33)SXI10, 12.2(33)SXI11, 12.2(33)SXI12, 12.2(33)SXI13, 12.2(33)SXI14, 12.4(3)JK4, 12.4(3)JK1, 12.4(3)JK, 12.4(3)JK3, 12.4(3)JK2, 12.2(44)SQ, 12.2(44)SQ2, 12.2(50)SQ2, 12.2(50)SQ1, 12.2(50)SQ, 12.2(50)SQ3, 12.2(50)SQ4, 12.2(50)SQ5, 12.2(50)SQ6, 12.2(50)SQ7, 12.2(33)SRE1, 12.2(33)SRE2, 12.2(33)SRE3, 12.2(33)SRE4, 12.2(33)SRE, 12.2(33)SRE0a, 12.2(33)SRE5, 12.2(33)SRE6, 12.2(33)SRE8, 12.2(33)SRE7, 12.2(33)SRE9, 12.2(33)SRE7a, 12.2(33)SRE10, 12.2(33)SRE11, 12.2(33)SRE9a, 12.2(33)SRE12, 12.2(33)SRE13, 12.2(33)SRE14, 12.2(33)SRE15, 12.2(33)SRE15a, 15.2(1)S, 15.2(2)S, 15.2(1)S1, 15.2(4)S, 15.2(1)S2, 15.2(2)S1, 15.2(2)S2, 15.2(2)S0a, 15.2(2)S0c, 15.2(4)S1, 15.2(4)S4, 15.2(4)S6, 15.2(4)S2, 15.2(4)S5, 15.2(4)S3, 15.2(4)S3a, 15.2(4)S4a, 15.2(4)S7, 15.3(1)T, 15.3(2)T, 15.3(1)T1, 15.3(1)T2, 15.3(1)T3, 15.3(1)T4, 15.3(2)T1, 15.3(2)T2, 15.3(2)T3, 15.3(2)T4, 15.0(1)EY, 15.0(1)EY1, 15.0(1)EY2, 15.0(2)EY, 15.0(2)EY1, 15.0(2)EY2, 15.0(2)EY3, 15.1(2)S, 15.1(1)S, 15.1(1)S1, 15.1(3)S, 15.1(1)S2, 15.1(2)S1, 15.1(2)S2, 15.1(3)S1, 15.1(3)S0a, 15.1(3)S2, 15.1(3)S4, 15.1(3)S3, 15.1(3)S5, 15.1(3)S6, 15.1(3)S5a, 15.1(4)M3, 15.1(4)M, 15.1(4)M1, 15.1(4)M2, 15.1(4)M6, 15.1(4)M5, 15.1(4)M4, 15.1(4)M7, 15.1(4)M3a, 15.1(4)M10, 15.1(4)M8, 15.1(4)M9, 15.0(1)SE, 15.0(2)SE, 15.0(1)SE1, 15.0(1)SE2, 15.0(1)SE3, 15.0(2)SE1, 15.0(2)SE2, 15.0(2)SE3, 15.0(2)SE4, 15.0(2)SE5, 15.0(2)SE6, 15.0(2)SE7, 15.0(2)SE8, 15.0(2)SE9, 15.0(2)SE10, 15.0(2)SE11, 15.0(2)SE10a, 15.0(2)SE12, 15.0(2)SE13, 15.1(2)GC, 15.1(2)GC1, 15.1(2)GC2, 15.1(4)GC, 15.1(4)GC1, 15.1(4)GC2, 15.0(1)SY, 15.0(1)SY1, 15.0(1)SY2, 15.0(1)SY3, 15.0(1)SY4, 15.0(1)SY5, 15.0(1)SY6, 15.0(1)SY7, 15.0(1)SY8, 15.0(1)SY7a, 15.0(1)SY9, 15.0(1)SY10, 12.2(33)SXJ, 12.2(33)SXJ1, 12.2(33)SXJ2, 12.2(33)SXJ3, 12.2(33)SXJ4, 12.2(33)SXJ5, 12.2(33)SXJ6, 12.2(33)SXJ7, 12.2(33)SXJ8, 12.2(33)SXJ9, 12.2(33)SXJ10, 15.1(1)SG, 15.1(2)SG, 15.1(1)SG1, 15.1(1)SG2, 15.1(2)SG1, 15.1(2)SG2, 15.1(2)SG3, 15.1(2)SG4, 15.1(2)SG5, 15.1(2)SG6, 15.1(2)SG7, 15.1(2)SG8, 15.2(4)M, 15.2(4)M1, 15.2(4)M2, 15.2(4)M4, 15.2(4)M3, 15.2(4)M5, 15.2(4)M8, 15.2(4)M10, 15.2(4)M7, 15.2(4)M6, 15.2(4)M9, 15.2(4)M6a, 15.2(4)M11, 15.0(2)SG, 15.0(2)SG1, 15.0(2)SG2, 15.0(2)SG3, 15.0(2)SG4, 15.0(2)SG5, 15.0(2)SG6, 15.0(2)SG7, 15.0(2)SG8, 15.0(2)SG9, 15.0(2)SG10, 15.0(2)SG11, 12.4(24)MDB, 12.4(24)MDB1, 12.4(24)MDB3, 12.4(24)MDB4, 12.4(24)MDB5, 12.4(24)MDB6, 12.4(24)MDB7, 12.4(24)MDB5a, 12.4(24)MDB8, 12.4(24)MDB9, 12.4(24)MDB10, 12.4(24)MDB11, 12.4(24)MDB12, 12.4(24)MDB13, 12.4(24)MDB14, 12.4(24)MDB15, 12.4(24)MDB16, 12.4(24)MDB17, 12.4(24)MDB18, 12.4(24)MDB19, 15.2(1)GC, 15.2(1)GC1, 15.2(1)GC2, 15.2(2)GC, 15.2(3)GC, 15.2(3)GC1, 15.2(4)GC, 15.2(4)GC1, 15.2(4)GC2, 15.2(4)GC3, 12.4(25d)JAX, 12.4(25d)JAX1, 12.4(25e)JAX, 12.4(25e)JAX1, 12.4(25e)JAX2, 12.2(33)SCG, 12.2(33)SCG1, 12.2(33)SCG2, 12.2(33)SCG3, 12.2(33)SCG4, 12.2(33)SCG5, 12.2(33)SCG6, 12.2(33)SCG7, 15.1(1)SY, 15.1(1)SY1, 15.1(2)SY, 15.1(2)SY1, 15.1(2)SY2, 15.1(1)SY2, 15.1(1)SY3, 15.1(2)SY3, 15.1(1)SY4, 15.1(2)SY4, 15.1(1)SY5, 15.1(2)SY5, 15.1(2)SY4a, 15.1(1)SY6, 15.1(2)SY6, 15.1(2)SY7, 15.1(2)SY8, 15.1(2)SY9, 15.1(2)SY10, 15.1(2)SY11, 15.1(2)SY12, 15.1(2)SY13, 15.1(2)SY14, 15.1(2)SY15, 15.1(2)SY16, 15.3(1)S,…
  • 1 additional product group retained in the authoritative source
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. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 25 Mar 2026 · Last source change 25 Mar 2026, 17:52 UTC · CWE-228 · Improper Handling of Syntactically Invalid Structure

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-2026-15449
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD awaiting enrichment

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

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2026-15449↗CVE authority or vendor reference · Cisco CISCO-SA-IOS-HTTP-DOS-SBV8XRPL↗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-2026-20125 · cve.blacktree.nl