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CVE Record

CVE-2021-40839: The rencode package through 1.0.6 for Python allows an infinite loop in typecode decoding (such as via ;\x2...

The rencode package through 1.0.6 for Python allows an infinite loop in typecode decoding (such as via ;\x2f\x7f), enabling a remote attack that consumes CPU and memory.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a denial-of-service issue in the Python rencode package. A specially malformed encoded value can make affected versions loop and consume CPU and memory. The main business risk is service instability where untrusted input is decoded with rencode.

Executive priority

Treat this as a targeted availability risk, not a confirmed breach indicator. Prioritize internet-facing or partner-facing services that parse rencode data, then apply vendor updates once exposure is confirmed.

Technical view

rencode through 1.0.6 has an infinite-loop condition in typecode decoding. If attacker-controlled serialized data reaches the decoder, processing can consume CPU and memory, causing denial of service. The source bundle does not provide CVSS, CWE, or a complete affected product list.

Likely exposure

Exposure is most likely in Python applications, packaged software, or appliances that include rencode through 1.0.6 and decode untrusted or remotely supplied data. NetApp and Fedora advisories indicate downstream ecosystem impact, but specific affected NetApp products are not listed in the prompt bundle.

Exploitation context

The CVE description says remote attack is possible through malformed encoded input. The bundle does not show CISA KEV listing or cited evidence of active exploitation, so active exploitation should not be claimed.

Researcher notes

The available evidence supports a resource-exhaustion flaw in decoder typecode handling and a fix reference in upstream GitHub. The prompt bundle does not establish exploit prevalence, CVSS scoring, or a definitive fixed release version.

Mitigation direction

  • Inventory direct and transitive use of Python rencode.
  • Prioritize systems decoding untrusted or remotely supplied rencode data.
  • Check rencode, Fedora, NetApp, and vendor guidance for fixed packages.
  • Apply relevant package or vendor updates where applicable.
  • Restrict or reject untrusted serialized input where updates are unavailable.

Validation and detection

  • Confirm deployed rencode versions are not through 1.0.6.
  • Review dependency lockfiles and packaged appliance advisories for bundled rencode.
  • Identify code paths that decode external rencode payloads.
  • Verify vendor updates are installed on affected Fedora or NetApp-managed systems.
  • Monitor affected services for abnormal CPU or memory exhaustion.
Prepared
Confidence
medium
Sources
9

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

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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
8Source 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

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