CVE-2021-41253

MEDIUMNVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.9 under NVD CVSS v3. EPSS exploit probability: 1.9% (78th percentile of EPSS-scored CVEs). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 1.9%CVSS: 5.9Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Zydis is an x86/x86-64 disassembler library. Users of Zydis versions v3.2.0 and older that use the string functions provided in zycore in order to append untrusted user data to the formatter buffer within their custom formatter hooks can run into heap buffer overflows. Older versions of Zydis failed to properly initialize the string object within the formatter buffer, forgetting to initialize a few fields, leaving their value to chance. This could then in turn cause zycore functions like ZyanStringAppend to make incorrect calculations for the new target size, resulting in heap memory corruption. This does not affect the regular uncustomized Zydis formatter, because Zydis internally doesn't use the string functions in zycore that act upon these fields. However, because the zycore string functions are the intended way to work with the formatter buffer for users of the library that wish to extend the formatter, we still consider this to be a vulnerability in Zydis. This bug is patched starting in version 3.2.1. As a workaround, users may refrain from using zycore string functions in their formatter hooks until updating to a patched version.

CVSS v3
5.9
EG Score
5.9MEDIUMmedium confidence
EG Risk
32
EG Risk 32/100CISA SSVC

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%
Exploitation2% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track or Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
1.9%
EPSS %ILE
78th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track or Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

November 8, 2021

Last Modified

November 21, 2024

References (8)

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
zydis—
  • every version up to 3.2.1-1: fixed in 3.2.1-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
zydis—
  • every version up to 3.2.1-1: fixed in 3.2.1-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
zydis—
  • every version up to 3.2.1-1: fixed in 3.2.1-1
—

Weakness Classification(3)

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

Data Freshness Timeline

(refreshed 6× in last 7d / 32× 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 188 total refreshes for this CVE.

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

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-41253?
CVE-2021-41253 is a medium vulnerability published on November 8, 2021. Zydis is an x86/x86-64 disassembler library. Users of Zydis versions v3.2.0 and older that use the string functions provided in zycore in order to append untrusted user data to the formatter buffer within their custom formatter hooks can run into heap buffer overflows. Older versions of Zydis…
When was CVE-2021-41253 disclosed?
CVE-2021-41253 was first published on November 8, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-41253 actively exploited?
CVE-2021-41253 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.9% probability of exploitation in the next 30 days (78th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-41253?
CVE-2021-41253 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2021-41253?
A fix for CVE-2021-41253 is available: update to the fixed version the vendor names in its advisory.

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