Evidence used
- No CISA KEV confirmation is currently recorded.
- Exploitation requires an existing local or physical foothold with privileges.
- EPSS is 0.10% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-16821High confidence
Vulnerabilities in IBM AIX and PowerVM VIOS
IBM · AIX
7.0HighCVSS 3.1
Within 7 days
Patch availableHigh technical severity; prioritise exposed affected systems while verifying vendor guidance.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityHigh→Operational priority:Medium, lowered one band.downgradedsince 1 Sep 2026
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict local access and enforce least privilege on affected hosts.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs IBM AIX and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Patch available01
What, why and how
IBM AIX 7.2, and 7.3 and IBM PowerVM VIOS 4.1 could allow a local attacker to gain elevated privileges due to a format string vulnerability.
What
IBM AIX 7.2, and 7.3 and IBM PowerVM VIOS 4.1 could allow a local attacker to gain elevated privileges due to a format string vulnerability.
Why
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How
An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may gain additional privileges.
What
IBM AIX 7.2, and 7.3 and IBM PowerVM VIOS 4.1 could allow a local attacker to gain elevated privileges due to a format string vulnerability.
Why
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How
An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may gain additional privileges.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.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 None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.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
- local access → Use of Externally-Controlled Format String → gain additional privileges
- Attack surface
- Local
- Privileges required
- Low: a basic authenticated account is required
- User interaction
- None
- Attack complexity
- High: exploitation depends on specific conditions
- 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-134 ↗
CWE-134: Use of Externally-Controlled Format String. The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:HCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRLowPrivileges required: The attacker needs basic user-level 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
- The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
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
- Fixed
- A. APARS
- IBM has assigned the following APARs to this problem:
- AIX LevelAPARAvailability SPKEY7.2.5IJ5956608/14/2026SP13key_w_apar7.3.2IJ5956508/14/2026SP05key_w_apar7.3.3IJ5956408/14/2026SP03key_w_apar7.3.4IJ59563 08/14/2026SP02key_w_apar
- VIOS LevelAPARAvailability SPKEY4.1.0IJ5956508/14/20264.1.0.50key_w_apar4.1.1IJ5956408/14/20264.1.1.30key_w_apar4.1.2IJ5956308/14/20264.1.2.20key_w_apar
- B. FIXES
- IBM strongly recommends addressing the vulnerability now.
- AIX and VIOS fixes are available and can be downloaded from Fix Central: https://www.ibm.com/support/fixcentral
- An LPAR reboot is required to complete the SP/FP update. On AIX, Live Update can be used to avoid a reboot.
- IBM has assigned the following AIX Service Packs (SPs) and VIOS Fix Packs (FPs) as the remediation levels for the published vulnerabilities.
- AIX Level Service PackAIX 7.3 TL04SP2AIX 7.3 TL03SP3AIX 7.3 TL02SP5AIX 7.2 TL05 SP13
- PowerVM VIOS LevelFix PackVIOS 4.1.2 4.1.2.20VIOS 4.1.1 4.1.1.30VIOS 4.1.0 4.1.0.50
- Note: These SPs/FPs are cumulative and include fixes for all previously published AIX/VIOS security vulnerabilities. They can be applied on top of any earlier affected level of the TL .
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. Limit untrusted access and use least privilege 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.
- Security Bulletin: Vulnerabilities in IBM AIX and PowerVM VIOS →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026IBM Support No results were found for your search query. Tips To return expected results, you can: Reduce the number of search terms. Each term you use focuses the search further. Check your spelling. A single misspelled or incorrectly typed term can change your result. Try substituting synonyms for your original ter
04
Evidence and provenance
Published 28 Aug 2026 · Last source change 1 Sept 2026, 03:56 UTC · CWE-134 · Use of Externally-Controlled Format String
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-29
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-67948
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Vendor guidanceAuthoritative vendor guidance changed: added patch: ibm.com/7283858; added remediation: ibm.com/7283858.psirt@us.ibm.com ↗
- Before
- no authoritative guidance recorded
- After
- patch: ibm.com/7283858 · remediation: ibm.com/7283858
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- 7.2; 7.3; 4.1 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
- After
- 7.2; 7.3; 4.1 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- Remediation statusRemediation status changed from Awaiting fix to Patch available.psirt@us.ibm.com ↗
- Before
- Awaiting fix
- After
- Patch available
- ENISA EUVD mappingEUVD-2026-67948 was added to the official ENISA EUVD mapping for this CVE.ENISA EUVD ↗
- Before
- not recorded
- After
- {"euvdId":"EUVD-2026-67948"}
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- 7.2; 7.3; 4.1 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- AIX: 7.2, 7.3; PowerVM VIOS: 4.1 · Fixed: A. APARS; IBM has assigned the following APARs to this problem:; AIX LevelAPARAvailability SPKEY7.2.5IJ5956608/14/2026SP13key_w_apar7.3.2IJ5956508/14/2026SP05key_w_apar7.3.3IJ5956408/14/2026SP03key_w_apar7.3.4IJ59563 08/14/2026SP02key_w_apar; VIOS LevelAPARAvailability SPKEY4.1.0IJ5956508/14/20264.1.0.50key_w_apar4.1.1IJ5956408/14/20264.1.1.30key_w_apar4.1.2IJ5956308/14/20264.1.2.20key_w_apar; B. FIXES; IBM strongly recommends addressing the vulnerability now.; AIX and VIOS fixes are available and can be downloaded from Fix Central: https://www.ibm.com/support/fixcentral; An LPAR reboot is required to complete the SP/FP update. On AIX, Live Update can be used to avoid a reboot.; IBM has assigned the following AIX Service Packs (SPs) and VIOS Fix Packs (FPs) as the remediation levels for the published vulnerabilities.; AIX Level Service PackAIX 7.3 TL04SP2AIX 7.3 TL03SP3AIX 7.3 TL02SP5AIX 7.2 TL05 SP13; PowerVM VIOS LevelFix PackVIOS 4.1.2 4.1.2.20VIOS 4.1.1 4.1.1.30VIOS 4.1.0 4.1.0.50; Note: These SPs/FPs are cumulative and include fixes for all previously published AIX/VIOS security vulnerabilities. They can be applied on top of any earlier affected level of the TL .
- Catalogue recordCVE added to the BlackTree catalogue.CNA ↗
CVE published
Fixed release or patch reference recorded
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.