CVE-2021-33304Network attack vector

Remote code execution via reassembled-frame double free

Published Feb 15, 2023 · Updated Mar 20, 2025

Double free in picoTCP 1.7.0 and picoTCP-NG 2.1 allows remote attackers to execute arbitrary code via fragmented network traffic. The pico_fragments_reassemble function calls pico_transport_receive, whose default branch discards the reassembled frame, and then discards the same frame again after the callee returns an error. No authentication or user interaction is required, and successful heap corruption grants code execution in the process embedding the stack.

CVSS severity9.8
Critical
EPSS probability0.84%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in picoTCP 1.7.0 and picoTCP-NG 2.1 allows remote attackers to execute arbitrary code via fragmented network traffic. The pico_fragments_reassemble function calls pico_transport_receive, whose default branch discards the reassembled frame, and then discards the same frame again after the callee returns an error. No authentication or user interaction is required, and successful heap corruption grants code execution in the process embedding the stack.

The record

CVE
CVE-2021-33304
Published
Feb 15, 2023
Updated
Mar 20, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-415
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 15, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 20, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-415Double Free

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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