CVE catalog

CVE-2021-41253

zydis affected and fixed versions

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.

Severity: Medium
Published: Nov 8, 2021, 10:15:00 PM UTC
Source: [NVD] · [CVE record]
EPSS: 1.86% · Oct 27, 2026

Projects and upstream resources

[zydis][Source-reported homepage]

Reported versions and fixes

Each observation applies to its named package, distribution, and release. Distribution backports can fix a vulnerability while retaining an older upstream version number.

Distribution / release	Package	Version	Status	Source
Debiantrixie	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debiantrixie	zydis	`4.1.1-1`	Fixed	[CVE-2021-41253]
Debiansid	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debiansid	zydis	`4.1.1-3`	Fixed	[CVE-2021-41253]
Debianforky	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debianforky	zydis	`4.1.1-3`	Fixed	[CVE-2021-41253]
Debianbookworm	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debianbookworm	zydis	`4.0.0-1`	Fixed	[CVE-2021-41253]

Provider details and historical evidence

Distribution / release	Package	Version	Status	Source
Debianbookworm	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debianbookworm	zydis	`4.0.0-1`	Fixed	[CVE-2021-41253]
Debianforky	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debianforky	zydis	`4.1.1-3`	Fixed	[CVE-2021-41253]
Debiansid	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debiansid	zydis	`4.1.1-3`	Fixed	[CVE-2021-41253]
Debiantrixie	zydis	`3.2.1-1`	FixedDistribution-reported fixed boundary	[CVE-2021-41253]
Debiantrixie	zydis	`4.1.1-1`	Fixed	[CVE-2021-41253]

Original provider fields

{
  "package_releases": [
    {
      "name": "zydis",
      "status": "fixed",
      "release": "sid",
      "version": "4.1.1-3"
    },
    {
      "name": "zydis",
      "status": "fixed",
      "release": "forky",
      "version": "4.1.1-3"
    },
    {
      "name": "zydis",
      "status": "fixed",
      "release": "trixie",
      "version": "4.1.1-1"
    },
    {
      "name": "zydis",
      "status": "fixed",
      "release": "bookworm",
      "version": "4.0.0-1"
    }
  ],
  "fixed_versions": [
    {
      "bug": 999431,
      "name": "zydis",
      "type": "source",
      "origin": null,
      "release": "sid",
      "urgency": "not yet assigned",
      "fixed_version": "3.2.1-1"
    },
    {
      "bug": 999431,
      "name": "zydis",
      "type": "source",
      "origin": null,
      "release": "forky",
      "urgency": "not yet assigned",
      "fixed_version": "3.2.1-1"
    },
    {
      "bug": 999431,
      "name": "zydis",
      "type": "source",
      "origin": null,
      "release": "trixie",
      "urgency": "not yet assigned",
      "fixed_version": "3.2.1-1"
    },
    {
      "bug": 999431,
      "name": "zydis",
      "type": "source",
      "origin": null,
      "release": "bookworm",
      "urgency": "not yet assigned",
      "fixed_version": "3.2.1-1"
    }
  ],
  "distribution_packages": []
}

[Debian bug #999431]

OpenFactory catalog packages

Matching against OpenFactory catalog package versions is in progress.

[Debian 12 (Bookworm)]

[libzydis4.0]Unknown
Source package: [zydis]
Details (2)
- 4.0.0-1 · amd64 · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
- 4.0.0-1 · arm64 · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
[libzydis-dev]Unknown
Source package: [zydis]
Details (2)
- 4.0.0-1 · amd64 · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
- 4.0.0-1 · arm64 · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
[libzydis-doc]Unknown
Source package: [zydis]
Details (2)
- 4.0.0-1 · all · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
- 4.0.0-1 · all · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
[zydis-tools]Unknown
Source package: [zydis]
Details (2)
- 4.0.0-1 · amd64 · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12
- 4.0.0-1 · arm64 · bookworm
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · bookworm; dsa · zydis · debian · 12

[Debian 13 (Trixie)]

[libzydis4.1]Unknown
Source package: [zydis]
Details (2)
- 4.1.1-1 · amd64 · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
- 4.1.1-1 · arm64 · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
[libzydis-dev]Unknown
Source package: [zydis]
Details (2)
- 4.1.1-1 · amd64 · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
- 4.1.1-1 · arm64 · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
[libzydis-doc]Unknown
Source package: [zydis]
Details (2)
- 4.1.1-1 · all · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
- 4.1.1-1 · all · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
[zydis-tools]Unknown
Source package: [zydis]
Details (2)
- 4.1.1-1 · amd64 · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13
- 4.1.1-1 · arm64 · trixie
  Fixed · Fixed: 3.2.1-1
  dsa · zydis · debian · 13

Observed: Oct 23, 2026, 6:02:43 PM UTC

References

[Debian Security Tracker] · [FIRST EPSS] · [OSV Package Vulnerability Database]