CVE-2026-40684

MEDIUMNVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

Score 5.9 from GitHub Security Advisory published 2026-05-01. NVD baseline CVSS 5.9; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dn_expand oddity in octal printing.

CVSS v3
5.9
EG Score
5.9(medium)
EG Risk
27(Track)
EG Risk 27/100SSVC: 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
Severity59% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
30%
KEV
Not listed

Published

April 30, 2026

Last Modified

May 1, 2026

Advisory Details (3)

Auto-updated Apr 30, 2026
No patch confirmed yet.
generic

oss-security - Exim 4.99.2 fixes 4 CVEs

https://www.openwall.com/lists/oss-security/2026/04/30/21
generic
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment
generic

Support musl libc dn_expand oddity · 628bbaca76 - exim/exim - Exim Forgejo

https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
exim44.100~RC1-1 ... 4.99~RC3-2 (121 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
exim44.96-15 ... 4.96-15+deb12u8 (9 versions)4.96-15+deb12u9—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
exim44.98.2-1, 4.98.2-1+deb13u14.98.2-1+deb13u2—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
exim44.98.2-1 ... 4.99~RC3-2 (25 versions)4.99.2-1—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 28× 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 176 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-40684?
CVE-2026-40684 is a medium vulnerability published on April 30, 2026. In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dn_expand oddity in octal printing.
When was CVE-2026-40684 disclosed?
CVE-2026-40684 was first published in the National Vulnerability Database on April 30, 2026, with the most recent update on May 1, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-40684 actively exploited?
CVE-2026-40684 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 70.4% of all scored CVEs.
What is the CVSS score of CVE-2026-40684?
CVE-2026-40684 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2026-40684?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-40684, 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.

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