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Full vulnerability report · 2021
CVE-2021-22991High confidence

F5 BIG-IP Traffic Management Microkernel Buffer Overflow

F5 · BIG-IP Traffic Management Microkernel

9.8CriticalCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2022-02-01 as the remediation due date.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

Evidence used

  • CISA confirms exploitation in the wild.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 61.06% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs F5 BIG-IP Traffic Management Microkernel and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  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-2021-10109

CISA KEV mirrored by ENISA

On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, and 12.1.x before 12.1.5.3, undisclosed requests to a virtual server may be incorrectly handled by the Traffic Management Microkernel (TMM) URI normalization, which may trigger a buffer overflow, resulting in a DoS attack. In certain situations, it may theoretically allow bypass of URL based access control or remote code execution (RCE). Note: Software versions which have reached End of Software Development (EoSD) are not evaluated.

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 18 Jan 2022. Evidence sources: cisa_kev.
ENISA score
9.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2022-02-01 as the remediation due date.

Patch available
01

What, why and how

The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.

What

The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.

Why

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

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

The Traffic Management Microkernel of BIG-IP ASM Risk Engine has a buffer overflow vulnerability, leading to a bypassing of URL-based access controls.

Why

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

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.

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 2022-01-18.

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 Restriction of Operations within the Bounds of a Memory Buffer → 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
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-119 ↗

CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer. The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

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:U/C:H/I:H/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.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.
NetworkUnauthenticatedCWE-119CISA KEV
A

Official authority intelligence

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

ENISA EUVD · EUVD-2021-10109Known-exploited evidence recorded

On BIG-IP versions 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, and 12.1.x before 12.1.5.3, undisclosed requests to a virtual server may be incorrectly handled by the Traffic Management Microkernel (TMM) URI normalization, which may trigger a buffer overflow, resulting in a DoS attack. In certain situations, it may theoretically allow bypass of URL based access control or remote code execution (RCE). Note: Software versions which have reached End of Software Development (EoSD) are not evaluated.

Official EUVD record ↗
Canadian Centre for Cyber Security · English · AL21-004Vulnerabilities impacting F5 BIG-IP and BIG-IQ - update 1

On 10 March 2021, F5 publicly disclosed details of critical vulnerabilities affecting BIG-IP, BIG-IP Advanced WAF/ASM, and BIG-IQ products. Neither F5 nor the Cyber Centre are aware of active exploitation of these vulnerabilities; however, due to their criticality it is advised to apply the necessary patches or mitigations immediately. UPDATE: As of 19 March 2021, the Cyber Centre has become aware of scanning and exploitation attempts against the iControl REST interface of F5 BIG-IP products within Canada. Successful exploitation could result in information disclosure or remote code execution which could lead to a full system compromise.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210407Security Bulletin 07 Apr 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 07 Apr 2021, published on 7 April 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-189Multiples vulnérabilités dans F5 BIG-IP

De multiples vulnérabilités ont été découvertes dans F5 BIG-IP. Certaines d'entre elles permettent à un attaquant de provoquer une exécution de code arbitraire à distance, un déni de service à distance et une atteinte à l'intégrité des données.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-005131BIG-IP における古典的バッファオーバーフローの脆弱性

BIG-IP には、古典的バッファオーバーフローの脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5279F5 BIG-IP 제품 보안 업데이트 권고

BIG-IP의 TMM에서 버퍼오버플로우로 인해 발생하는 원격코드실행 취약점(CVE-2021-22991)

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.
Patch available
Affected
BIG-IP: 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3
Fixed
The Cyber Centre recommends organizations review all impacted F5 appliances and virtual deployments and patch to one of the below recommended versions. [ 1 ] BIG-IP: Versions 16.0.0 to 16.0.1 should be upgraded to 16.0.1.1 Versions 15.1.0 to 15.1.2 should be upgraded to 15.1.2.1 Versions 14.1.0 to 14.1.3.1 should be upgraded to 14.1.4 Versions 13.1.0 to 13.1.3.5 should be upgraded to 13.1.3.6 Versions 12.1.0 to 12.1.5.2 should be upgraded to 12.1.5.3 Versions 11.6.1 to 11.6.5.2 should be upgraded to 11.6.5.3 BIG-IQ: Version 8.0.0 is unaffected Versions 7.1.0 to 7.1.0.2 should be upgraded to 8.0.0 Versions 7.0.0 to 7.0.0.1 should be upgraded to 7.1.0.3 Versions 6.0.0 to 6.1.0 should be upgraded to 7.0.0.2 F5 indicates that if a fixed version has not been identified for a branch used by an organization then no update is available. F5 recommends that organizations upgrade to a version with an available patch. Organizations may use the F5 platform matrix to determine compatible software versions for their F5 platform. [ 1 ] While the Cyber Centre strongly encourages patching as soon as possible, administrators should consider applying the mitigations described in the F5 KB articles if patching is not immediately possible. See the [ 4 ] and [ 5 ] for more details. In summary: Block iControl REST access through the self IP address. Block iControl REST access through the management interface. Block Configuration utility access through self IP addresses. Block Configuration utility access through the management interface. Patching as described in this section also fixes the buffer overflow vulnerabilities described in the previous section. There are no mitigations against CVE-2021-22991 other than patching, while for CVE-2021-22992 F5 has provided an iRule mitigation. [ 9 ] In all cases, the Cyber Centre and F5 recommend patching as the primary mitigation.
Action
Apply the fixed release for the affected product branch as recorded by Canadian Centre for Cyber Security. Validate the exact product and build in the linked advisory before deployment.
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 31 Mar 2021 · Last source change 21 Oct 2025, 23:25 UTC · CWE-119 · Improper Restriction of Operations within the Bounds of a Memory Buffer

CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
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-2021-10109
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCISA ADP
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. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/vulnerabilities-impacting-f5-big-ip-and-big-iq.
    Before
    remediation: cyber.gc.ca/vulnerabilities-impacting-f5-big-ip-and-big-iq · vendor advisory: support.f5.com/K56715231
    After
    vendor advisory: support.f5.com/K56715231
    support.f5.com ↗
  2. Affected versionsThe structured affected or fixed version information changed.
    Before
    BIG-IP: 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3 · Fixed: The Cyber Centre recommends organizations review all impacted F5 appliances and virtual deployments and patch to one of the below recommended versions. [ 1 ] BIG-IP: Versions 16.0.0 to 16.0.1 should be upgraded to 16.0.1.1 Versions 15.1.0 to 15.1.2 should be upgraded to 15.1.2.1 Versions 14.1.0 to 14.1.3.1 should be upgraded to 14.1.4 Versions 13.1.0 to 13.1.3.5 should be upgraded to 13.1.3.6 Versions 12.1.0 to 12.1.5.2 should be upgraded to 12.1.5.3 Versions 11.6.1 to 11.6.5.2 should be upgraded to 11.6.5.3 BIG-IQ: Version 8.0.0 is unaffected Versions 7.1.0 to 7.1.0.2 should be upgraded to 8.0.0 Versions 7.0.0 to 7.0.0.1 should be upgraded to 7.1.0.3 Versions 6.0.0 to 6.1.0 should be upgraded to 7.0.0.2 F5 indicates that if a fixed version has not been identified for a branch used by an organization then no update is available. F5 recommends that organizations upgrade to a version with an available patch. Organizations may use the F5 platform matrix to determine compatible software versions for their F5 platform. [ 1 ] While the Cyber Centre strongly encourages patching as soon as possible, administrators should consider applying the mitigations described in the F5 KB articles if patching is not immediately possible. See the [ 4 ] and [ 5 ] for more details. In summary: Block iControl REST access through the self IP address. Block iControl REST access through the management interface. Block Configuration utility access through self IP addresses. Block Configuration utility access through the management interface. Patching as described in this section also fixes the buffer overflow vulnerabilities described in the previous section. There are no mitigations against CVE-2021-22991 other than patching, while for CVE-2021-22992 F5 has provided an iRule mitigation. [ 9 ] In all cases, the Cyber Centre and F5 recommend patching as the primary mitigation.
    After
    BIG-IP: 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CISA KEV ↗
  3. Remediation statusRemediation status changed from Patch available to Awaiting fix.
    Before
    Patch available
    After
    Awaiting fix
    support.f5.com ↗
  4. Affected versionsThe structured affected or fixed version information changed.
    Before
    16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    BIG-IP: 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CNA ↗
  5. Affected versionsThe structured affected or fixed version information changed.
    Before
    BIG-IP: 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    BIG-IP: 16.0.x before 16.0.1.1, 15.1.x before 15.1.2.1, 14.1.x before 14.1.4, 13.1.x before 13.1.3.6, 12.1.x before 12.1.5.3 · Fixed: The Cyber Centre recommends organizations review all impacted F5 appliances and virtual deployments and patch to one of the below recommended versions. [ 1 ] BIG-IP: Versions 16.0.0 to 16.0.1 should be upgraded to 16.0.1.1 Versions 15.1.0 to 15.1.2 should be upgraded to 15.1.2.1 Versions 14.1.0 to 14.1.3.1 should be upgraded to 14.1.4 Versions 13.1.0 to 13.1.3.5 should be upgraded to 13.1.3.6 Versions 12.1.0 to 12.1.5.2 should be upgraded to 12.1.5.3 Versions 11.6.1 to 11.6.5.2 should be upgraded to 11.6.5.3 BIG-IQ: Version 8.0.0 is unaffected Versions 7.1.0 to 7.1.0.2 should be upgraded to 8.0.0 Versions 7.0.0 to 7.0.0.1 should be upgraded to 7.1.0.3 Versions 6.0.0 to 6.1.0 should be upgraded to 7.0.0.2 F5 indicates that if a fixed version has not been identified for a branch used by an organization then no update is available. F5 recommends that organizations upgrade to a version with an available patch. Organizations may use the F5 platform matrix to determine compatible software versions for their F5 platform. [ 1 ] While the Cyber Centre strongly encourages patching as soon as possible, administrators should consider applying the mitigations described in the F5 KB articles if patching is not immediately possible. See the [ 4 ] and [ 5 ] for more details. In summary: Block iControl REST access through the self IP address. Block iControl REST access through the management interface. Block Configuration utility access through self IP addresses. Block Configuration utility access through the management interface. Patching as described in this section also fixes the buffer overflow vulnerabilities described in the previous section. There are no mitigations against CVE-2021-22991 other than patching, while for CVE-2021-22992 F5 has provided an iRule mitigation. [ 9 ] In all cases, the Cyber Centre and F5 recommend patching as the primary mitigation.
    Canadian Centre for Cyber Security ↗
  6. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    Canadian Centre for Cyber Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2021-10109↗Canadian Centre for Cyber Security remediation guidance↗CISA KEV record↗CVE authority or vendor 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-2021-22991 · cve.blacktree.nl