CVE-2026-23409

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2026-04-01. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.5Exploit: None knownExposed: 0

A fix is available — apply it.

In the Linux kernel, the following vulnerability has been resolved:

apparmor: fix differential encoding verification

Differential encoding allows loops to be created if it is abused. To prevent this the unpack should verify that a diff-encode chain terminates.

Unfortunately the differential encode verification had two bugs.

  • it conflated states that had gone through check and already been
marked, with states that were currently being checked and marked. This means that loops in the current chain being verified are treated as a chain that has already been verified.
  • the order bailout on already checked states compared current chain
check iterators j,k instead of using the outer loop iterator i. Meaning a step backwards in states in the current chain verification was being mistaken for moving to an already verified state.

Move to a double mark scheme where already verified states get a different mark, than the current chain being kept. This enables us to also drop the backwards verification check that was the cause of the second error as any already verified state is already marked.

CVSS v3
5.5
EG Score
5.5(medium)
EG Risk
29(Track)
EG Risk 29/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity55% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
7%
KEV
Not listed

Published

April 1, 2026

Last Modified

April 24, 2026

Advisory Details (8)

Auto-updated Aug 6, 2026
No patch confirmed yet.
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/ff7c73744fafe944ed9a7b2b7cf6c8d5557a3d84
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/f90e3ecd9e1ed69f1a370f866ceed1f104f3ab4a
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/623a9d211bbbb031bb1cbdb38b23487648167f8a
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/39440b137546a3aa383cfdabc605fb73811b6093
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/34fc60b125ed1d4eb002c76b0664bf0619492167
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/1ff4857fac56ac5a90ee63b24db05fa5e91a45aa
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/1439150cd3c411228b387ab5efca92199d2a659a
generic

apparmor: fix differential encoding verification - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/0fab44285445e9012674396d5c1236a67da518e0

Vendor Advisories for CVE-2026-23409(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(11)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-tools-intel-iot-realtime-5.15 (5.15.0.1096.100) @ jammy2026-06-11ubuntu
ubuntulinux-tools-azure-fips-6.8 (6.8.0-1052.58+fips1) @ noble2026-06-11ubuntu
ubuntulinux-tools-azure-fips-5.15 (5.15.0.1109.94) @ jammy2026-06-11ubuntu
ubuntulinux-tools-raspi2-hwe-18.04-edge (5.4.0.1139.170) @ focal2026-06-11ubuntu
ubuntulinux-tools-azure-edge (5.15.0.1110.119~20.04.1) @ focal2026-06-11ubuntu
ubuntulinux-xilinx-zynqmp (6.8.0.1029.30) @ noble2026-06-11ubuntu
ubuntulinux-tools-bluefield-5.4 (5.4.0.1116.112) @ focal2026-06-11ubuntu
ubuntulinux-tools-azure-edge (5.4.0.1161.167~18.04.1) @ bionic2026-06-11ubuntu
ubuntulinux-tools-oem-6.17 (6.17.0-1017.17) @ noble2026-06-11ubuntu
ubuntulinux-tools-azure-lts-22.04 (5.15.0.1109.107) @ jammy2026-06-11ubuntu
linuxKernel @ 5.10.253—osv

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
linux5.10.103-1 ... 5.10.92-2 (49 versions)5.10.251-1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
linux6.1.106-1 ... 6.1.99-1 (47 versions)6.1.164-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
linux6.12.38-1 ... 6.12.74-2~bpo12+1 (15 versions)6.12.74-2—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
linux6.12.100-1 ... 6.19~rc8-1~exp1 (118 versions)6.19.6-2—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(10)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 5× in last 7d / 27× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 206 total refreshes for this CVE.

  1. 2026-09-13 16:47 UTCEPSS rescore
  2. 2026-09-12 15:01 UTCEPSS rescore
  3. 2026-09-11 14:52 UTCEPSS rescore
  4. 2026-09-10 09:34 UTCEPSS rescore
  5. 2026-09-08 22:00 UTCEPSS rescore
  6. 2026-09-07 16:01 UTCEPSS rescore
  7. 2026-09-06 13:47 UTCEPSS rescore
  8. 2026-09-06 13:47 UTCEPSS rescore
  9. 2026-09-04 05:06 UTCEPSS rescore
  10. 2026-09-02 14:11 UTCEPSS rescore
  11. 2026-09-02 11:44 UTCOSV refresh
  12. 2026-09-01 13:53 UTCEPSS rescore
  13. 2026-09-01 04:39 UTCEPSS rescore
  14. 2026-08-30 19:17 UTCEPSS rescore
  15. 2026-08-30 01:22 UTCEPSS rescore
  16. 2026-08-28 21:41 UTCEPSS rescore
  17. 2026-08-27 14:25 UTCEPSS rescore
  18. 2026-08-26 14:46 UTCEPSS rescore
  19. 2026-08-23 00:19 UTCEPSS rescore
  20. 2026-08-21 23:49 UTCEPSS rescore
  21. 2026-08-19 17:03 UTCEPSS rescore
  22. 2026-08-18 13:48 UTCEPSS rescore
  23. 2026-08-17 13:47 UTCEPSS rescore
  24. 2026-08-16 14:56 UTCEPSS rescore
  25. 2026-08-16 09:32 UTCEG score recompute
Show 75 more
  1. 2026-08-16 09:32 UTCVendor advisory
  2. 2026-08-16 09:32 UTCGHSA enrichment
  3. 2026-08-16 02:14 UTCEPSS rescore
  4. 2026-08-15 01:30 UTCEPSS rescore
  5. 2026-08-14 05:57 UTCEG score recompute
  6. 2026-08-14 05:57 UTCVendor advisory
  7. 2026-08-14 05:57 UTCGHSA enrichment
  8. 2026-08-13 22:00 UTCEPSS rescore
  9. 2026-08-12 20:14 UTCEG score recompute
  10. 2026-08-12 20:14 UTCVendor advisory
  11. 2026-08-12 20:14 UTCGHSA enrichment
  12. 2026-08-12 13:50 UTCEPSS rescore
  13. 2026-08-11 13:42 UTCEPSS rescore
  14. 2026-08-11 06:43 UTCEG score recompute
  15. 2026-08-11 06:43 UTCVendor advisory
  16. 2026-08-11 06:43 UTCGHSA enrichment
  17. 2026-08-11 00:00 UTCEPSS rescore
  18. 2026-08-10 06:10 UTCEG score recompute
  19. 2026-08-10 06:10 UTCVendor advisory
  20. 2026-08-10 06:10 UTCGHSA enrichment
  21. 2026-08-09 13:46 UTCEPSS rescore
  22. 2026-08-09 05:31 UTCEG score recompute
  23. 2026-08-09 05:31 UTCVendor advisory
  24. 2026-08-09 05:31 UTCGHSA enrichment
  25. 2026-08-08 16:37 UTCEPSS rescore
  26. 2026-08-07 15:37 UTCEG score recompute
  27. 2026-08-07 15:37 UTCVendor advisory
  28. 2026-08-07 15:37 UTCGHSA enrichment
  29. 2026-08-06 13:46 UTCEPSS rescore
  30. 2026-08-06 00:31 UTCEG score recompute
  31. 2026-08-06 00:31 UTCVendor advisory
  32. 2026-08-06 00:30 UTCGHSA enrichment
  33. 2026-08-05 19:17 UTCEPSS rescore
  34. 2026-08-04 15:10 UTCEPSS rescore
  35. 2026-08-04 10:38 UTCEPSS rescore
  36. 2026-08-03 22:51 UTCEG score recompute
  37. 2026-08-03 22:51 UTCVendor advisory
  38. 2026-08-03 22:51 UTCGHSA enrichment
  39. 2026-08-03 10:35 UTCEPSS rescore
  40. 2026-08-02 14:50 UTCEG score recompute
  41. 2026-08-02 14:50 UTCVendor advisory
  42. 2026-08-02 14:50 UTCGHSA enrichment
  43. 2026-08-02 02:26 UTCEPSS rescore
  44. 2026-08-01 04:15 UTCEPSS rescore
  45. 2026-07-30 01:30 UTCEPSS rescore
  46. 2026-07-27 14:13 UTCEPSS rescore
  47. 2026-07-26 14:54 UTCEPSS rescore
  48. 2026-07-26 14:54 UTCEPSS rescore
  49. 2026-07-25 14:17 UTCEPSS rescore
  50. 2026-07-25 14:17 UTCEPSS rescore
  51. 2026-07-24 14:17 UTCEPSS rescore
  52. 2026-07-23 14:18 UTCEPSS rescore
  53. 2026-07-23 14:18 UTCEPSS rescore
  54. 2026-07-23 03:07 UTCEG score recompute
  55. 2026-07-22 14:08 UTCEPSS rescore
  56. 2026-07-21 15:24 UTCEPSS rescore
  57. 2026-07-21 15:24 UTCEPSS rescore
  58. 2026-07-20 17:08 UTCEPSS rescore
  59. 2026-07-19 14:31 UTCEPSS rescore
  60. 2026-07-19 14:31 UTCEPSS rescore
  61. 2026-07-19 02:29 UTCEPSS rescore
  62. 2026-07-19 02:28 UTCEPSS rescore
  63. 2026-07-18 10:04 UTCEPSS rescore
  64. 2026-07-18 10:04 UTCEPSS rescore
  65. 2026-07-17 04:24 UTCOSV refresh
  66. 2026-07-16 17:03 UTCEPSS rescore
  67. 2026-07-16 17:03 UTCEPSS rescore
  68. 2026-07-15 16:57 UTCEPSS rescore
  69. 2026-07-15 16:57 UTCEPSS rescore
  70. 2026-07-15 02:00 UTCEPSS rescore
  71. 2026-07-15 02:00 UTCEPSS rescore
  72. 2026-07-13 22:30 UTCEPSS rescore
  73. 2026-07-13 06:13 UTCEPSS rescore
  74. 2026-07-13 06:13 UTCEPSS rescore
  75. 2026-07-12 05:46 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-23409?
CVE-2026-23409 is a medium vulnerability published on April 1, 2026. In the Linux kernel, the following vulnerability has been resolved: apparmor: fix differential encoding verification Differential encoding allows loops to be created if it is abused. To prevent this the unpack should verify that a diff-encode chain terminates. Unfortunately the differential encode…
When was CVE-2026-23409 disclosed?
CVE-2026-23409 was first published in the National Vulnerability Database on April 1, 2026, with the most recent update on April 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-23409 actively exploited?
CVE-2026-23409 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 92.6% of all scored CVEs.
What is the CVSS score of CVE-2026-23409?
CVE-2026-23409 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2026-23409?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-23409, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-23409

Explore →

Is Your Infrastructure Affected by CVE-2026-23409?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs