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Full vulnerability report · 2024
CVE-2021-47607High confidence

bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg

Linux · Linux

5.5MediumCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 184 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Low, lowered one band.downgradedsince 11 May 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 0.25% for the current model date.

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

  1. Confirm that the asset runs Linux Linux 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: No default targetRemediation target: Normal maintenance

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.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 184 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.15-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.15-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.15-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.15-1Debian Security Tracker ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2021-47607 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitykernel: bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg
184 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • bpftool as a component of Red Hat Enterprise Linux 7
  • kernel as a component of Red Hat Enterprise Linux 7
  • kernel-abi-whitelists as a component of Red Hat Enterprise Linux 7
  • kernel-bootwrapper as a component of Red Hat Enterprise Linux 7
  • kernel-debug as a component of Red Hat Enterprise Linux 7
  • kernel-debug-devel as a component of Red Hat Enterprise Linux 7
  • kernel-devel as a component of Red Hat Enterprise Linux 7
  • kernel-doc as a component of Red Hat Enterprise Linux 7
  • kernel-headers as a component of Red Hat Enterprise Linux 7
  • kernel-kdump as a component of Red Hat Enterprise Linux 7
  • kernel-kdump-devel as a component of Red Hat Enterprise Linux 7
  • kernel-rt as a component of Red Hat Enterprise Linux 7
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg The implementation of BPF_CMPXCHG on a high level has the following parameters: .-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) `-[mem-loc] `-[old-val] Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value. Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address. Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.
Remediation
Fix deferred
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-2021-34609

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 actionPatch only the product branches with a verified fix

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 184 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg The implementation of BPF_CMPXCHG on a high level has the following parameters: .-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) `-[mem-loc] `-[old-val] Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value. Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address. Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.

What

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg The implementation of BPF_CMPXCHG on a high level has the following parameters: .-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) `-[mem-loc] `-[old-val] Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value. Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address. Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg The implementation of BPF_CMPXCHG on a high level has the following parameters: .-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) `-[mem-loc] `-[old-val] Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value. Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address. Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through local access may attempt exploitation with low privileges. 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.
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
local access → vulnerable operation → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Local
Privileges required
Low: a basic authenticated account is required
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.
CWE not yet assigned
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:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Common 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.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.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.INoneIntegrity impact: No direct loss is represented by this metric.ANoneAvailability impact: No direct loss is represented by this metric.
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.
A

Official authority intelligence

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

BSI · German · WID-SEC-2024-1418Linux Kernel: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

Ein lokaler Angreifer kann mehrere Schwachstellen im Linux Kernel ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20240626Security Bulletin 26 Jun 2024

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 26 Jun 2024, published on 26 June 2024. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2025-AVI-1057Multiples vulnérabilités dans les produits VMware

d?id=CVE-2021-47539 Référence CVE CVE-2021-47550 https://www.cve.org/CVERecord?id=CVE-2021-47550 Référence CVE CVE-2021-47559 https://www.cve.org/CVERecord?id=CVE-2021-47559 Référence CVE CVE-2021-47561 https://www.cve.org/CVERecord?id=CVE-2021-47561 Référence CVE CVE-2021-47572 https://www.cve.org/CVERecord?id=CVE-2021-47572 Référence CVE CVE-2021-47576 https://www.cve.org/CVERecord?id=CVE-2021-47576 Référence CVE CVE-2021-47578 https://www.cve.org/CVERecord?id=CVE-2021-47578 Référence CVE CVE-2021-47579 https://www.cve.org/CVERecord?id=CVE-2021-47579 Référence CVE CVE-2021-47601 https://www.cve.org/CVERecord?id=CVE-2021-47601 Référence CVE CVE-2021-47607 https://www.cve.org/CVERecord?id=CVE-2021-47607 Référence CVE CVE-2021-47609 https://www.cve.org/CVERecord?id=CVE-2021-47609 Référence CVE CVE-2021-47613 https://www.cve.org/CVERecord?id=CVE-2021-47613 Référence CVE CVE-2021-47616 https://www.cve.org/CVERecord?id=CVE-2021-47616 Référence CVE CVE-2021-47617 https://www.cve.org/CVERecord?id=CVE-2021-47617 Référence CVE CVE-2021-47620 https://www.cve.org/CVERecord?id=CVE-2021-47620 Référence CVE CVE-2021-47623 https://www.cve.org/CVERecord?id=CVE-2021-47623 Référence CVE CVE-2021-47648 https://www.cve.org/CVERecord?id=CVE-2021-47648 Référence CVE CVE-2021-47649 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0693Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47598 Référence CVE CVE-2021-47599 https://www.cve.org/CVERecord?id=CVE-2021-47599 Référence CVE CVE-2021-47600 https://www.cve.org/CVERecord?id=CVE-2021-47600 Référence CVE CVE-2021-47601 https://www.cve.org/CVERecord?id=CVE-2021-47601 Référence CVE CVE-2021-47602 https://www.cve.org/CVERecord?id=CVE-2021-47602 Référence CVE CVE-2021-47603 https://www.cve.org/CVERecord?id=CVE-2021-47603 Référence CVE CVE-2021-47604 https://www.cve.org/CVERecord?id=CVE-2021-47604 Référence CVE CVE-2021-47605 https://www.cve.org/CVERecord?id=CVE-2021-47605 Référence CVE CVE-2021-47606 https://www.cve.org/CVERecord?id=CVE-2021-47606 Référence CVE CVE-2021-47607 https://www.cve.org/CVERecord?id=CVE-2021-47607 Référence CVE CVE-2021-47608 https://www.cve.org/CVERecord?id=CVE-2021-47608 Référence CVE CVE-2021-47609 https://www.cve.org/CVERecord?id=CVE-2021-47609 Référence CVE CVE-2021-47610 https://www.cve.org/CVERecord?id=CVE-2021-47610 Référence CVE CVE-2021-47611 https://www.cve.org/CVERecord?id=CVE-2021-47611 Référence CVE CVE-2021-47612 https://www.cve.org/CVERecord?id=CVE-2021-47612 Référence CVE CVE-2021-47614 https://www.cve.org/CVERecord?id=CVE-2021-47614 Référence CVE CVE-2021-47615 https://www.cve.org/CVERecord?id=CVE-2021-47615 Référence CVE CVE-2021-47616 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0578Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47595 Référence CVE CVE-2021-47596 https://www.cve.org/CVERecord?id=CVE-2021-47596 Référence CVE CVE-2021-47597 https://www.cve.org/CVERecord?id=CVE-2021-47597 Référence CVE CVE-2021-47600 https://www.cve.org/CVERecord?id=CVE-2021-47600 Référence CVE CVE-2021-47601 https://www.cve.org/CVERecord?id=CVE-2021-47601 Référence CVE CVE-2021-47602 https://www.cve.org/CVERecord?id=CVE-2021-47602 Référence CVE CVE-2021-47603 https://www.cve.org/CVERecord?id=CVE-2021-47603 Référence CVE CVE-2021-47604 https://www.cve.org/CVERecord?id=CVE-2021-47604 Référence CVE CVE-2021-47605 https://www.cve.org/CVERecord?id=CVE-2021-47605 Référence CVE CVE-2021-47607 https://www.cve.org/CVERecord?id=CVE-2021-47607 Référence CVE CVE-2021-47608 https://www.cve.org/CVERecord?id=CVE-2021-47608 Référence CVE CVE-2021-47609 https://www.cve.org/CVERecord?id=CVE-2021-47609 Référence CVE CVE-2021-47610 https://www.cve.org/CVERecord?id=CVE-2021-47610 Référence CVE CVE-2021-47611 https://www.cve.org/CVERecord?id=CVE-2021-47611 Référence CVE CVE-2021-47612 https://www.cve.org/CVERecord?id=CVE-2021-47612 Référence CVE CVE-2021-47614 https://www.cve.org/CVERecord?id=CVE-2021-47614 Référence CVE CVE-2021-47615 https://www.cve.org/CVERecord?id=CVE-2021-47615 Référence CVE CVE-2021-47616 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-021306Linux の Linux Kernel における脆弱性

Linux の Linux Kernel には、不特定の脆弱性が存在します。

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 availability varies by product
Affected
Fixed
Linux: < 5.12, 5.15.11 ≤ 5.15.*, 5.16 ≤ *
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. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 19 Jun 2024 · Last source change 11 May 2026, 13:57 UTC · CWE not yet assigned

CVE recordCVE.org · 5.2
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-2021-34609
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceUnavailable
NVD statusNVD modified after enrichment

Missing structured fields: CWE classification. Missing data is not evidence of low risk; review the primary advisory.

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
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-34609↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Patch or update 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-2021-47607 · cve.blacktree.nl