LiveActive security incident?Get immediate response
CVE Record

CVE-2021-36159: libfetch before 2021-07-26, as used in apk-tools, xbps, and other products, mishandles numeric strings for...

libfetch before 2021-07-26, as used in apk-tools, xbps, and other products, mishandles numeric strings for the FTP and HTTP protocols. The FTP passive mode implementation allows an out-of-bounds read because strtol is used to parse the relevant numbers into address bytes. It does not check if the line ends prematurely. If it does, the for-loop condition checks for the '\0' terminator one byte too late.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-36159 is a parsing flaw in libfetch before 2021-07-26. A malformed FTP or HTTP numeric string can make the library read outside expected memory. Business risk depends on where libfetch is embedded, such as package tools or container images, and whether those clients contact untrusted endpoints.

Executive priority

Treat this as a dependency hygiene issue until local exposure is confirmed. Prioritize container and package-management environments because vulnerable tooling may run during builds or updates, but the public data here does not justify emergency response without confirmed presence.

Technical view

The CVE describes libfetch mishandling numeric strings for FTP and HTTP. In FTP passive mode, strtol parses numbers into address bytes without correctly handling premature line endings, causing an out-of-bounds read. The bundle names apk-tools, xbps, and other products as consumers, but does not provide CVSS, CWE, or complete affected-version data.

Likely exposure

Exposure is most likely in systems, containers, or package workflows using libfetch before 2021-07-26, including apk-tools or xbps where present. The provided data does not enumerate complete affected products or versions.

Exploitation context

The source bundle does not show KEV listing, public active exploitation, or weaponized use. Exploitation would require a vulnerable libfetch client to process a malformed FTP or HTTP response from an endpoint or path it reaches.

Researcher notes

Evidence is limited. The strongest technical detail is the FTP passive-mode out-of-bounds read from premature numeric-string termination. The bundle also mentions HTTP numeric-string handling but gives less detail. No source here supports RCE, privilege escalation, or active exploitation claims.

Mitigation direction

  • Inventory libfetch usage in operating systems, containers, and package tooling.
  • Upgrade libfetch or vendor packages to versions incorporating post-2021-07-26 fixes.
  • Check apk-tools, xbps, and image vendor advisories for fixed builds.
  • Reduce reliance on untrusted FTP or HTTP endpoints where feasible.
  • Rebuild affected container images after base image updates.

Validation and detection

  • Confirm installed libfetch package versions or build dates against vendor advisories.
  • Check whether apk-tools or xbps are present in deployed images.
  • Review vulnerability scanner findings for CVE-2021-36159 in base images.
  • Confirm updated images no longer report vulnerable libfetch components.
  • Document any remaining exposure where vendor fixed-version data is unavailable.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-36159 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.