Cyber Resilience

CVE-2026-81727

Public PoC
Published
27 August 2026
Modified
28 August 2026
CVSS Score v4 6.9
Click a component to see what it means
Raw vectorCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0014 3th percentile
Risk Priority 28 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-81727 is a medium-severity Link Following (CWE-59) vulnerability. Its CVSS base score is 6.9 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Path Interception (T1034); ranked at the 3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-6 (Least Privilege) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access Control

EU & UK References

Vulnerability Data

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create…

more

hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.

CWE(s)
CWE-59

Related Threats

MITRE ATT&CK Enterprise Techniques

T1034 Path Interception Persistence
**This technique has been deprecated.
attack.mitre.org →
T1547.009 Shortcut Modification Persistence
Adversaries may create or modify shortcuts that can execute a program during system boot or user login.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-35025Shared CWE-59
CVE-2023-27469Shared CWE-59
CVE-2019-1385Shared CWE-59
CVE-2023-36723Shared CWE-59
CVE-2026-28866Shared CWE-59
CVE-2024-56074Shared CWE-59
CVE-2025-15313Shared CWE-59
CVE-2024-12390Shared CWE-59
CVE-2026-35400Shared CWE-59
CVE-2023-20004Shared CWE-59

Affected Assets

—
NLTK
inferred from references and description; NVD did not file a CPE for this CVE

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V15.4.2

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

Proper enforcement of access authorizations on the resolved target resource stops a link from reaching an unintended object.

AC-6 Least Privilege partial match

Least-privilege limits the damage an attacker can cause after following an unintended link.

SI-10 Information Input Validation partial match

Validating file-name inputs can reject or canonicalize names that resolve to links before access occurs.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require code to validate paths and avoid unsafe link following.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect link-following flaws before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC practices can mandate link-resolution checks and canonicalization before file access.

A.8.26 Application security requirements partial match
prevents

Application security requirements can explicitly require safe handling of symbolic links and path traversal.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include input validation and safe file-access design patterns.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly address canonicalization and symlink attacks during implementation.

A.8.3 Information access restriction none match
mitigates

Access-control rules can limit which files are reachable, reducing exposure to malicious links.

References