CVE-2021-33304: Double Free vulnerability in virtualsquare picoTCP v1.7.0 and picoTCP-NG v2.1 in modules/pico_fragments.c in f

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CRITICAL 9.8REMOTEDOWNGRADEDOWNGRADE

CVE-2021-33304 is a critical-severity flaw (CVSS 9.8) affecting picotcp, picotcp-ng. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Double Free vulnerability in virtualsquare picoTCP v1.7.0 and picoTCP-NG v2.1 in modules/pico_fragments.c in function pico_fragments_reassemble, allows attackers to execute arbitrary code.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.8% (top 42%)
CISA exploited list	No
Weakness	CWE-415
Published	2023-02-15
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: altran

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2023-02-15 22:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

altran picotcp DOWNGRADE

Affected: 1.7.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.7.0

1. Check installed version

apt-cache policy picotcp || rpm -q picotcp || picotcp --version

2. No fixed release: DOWNGRADE to a release before 1.7.0 (Debian / Ubuntu)

apt-cache madison picotcp sudo apt install picotcp=<VERSION_BEFORE_1.7.0> sudo apt-mark hold picotcp

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list picotcp sudo dnf downgrade picotcp-<VERSION_BEFORE_1.7.0> sudo dnf versionlock add picotcp

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

altran picotcp-ng DOWNGRADE

Affected: 2.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.1

1. Check installed version

apt-cache policy picotcp-ng || rpm -q picotcp-ng || picotcp-ng --version

2. No fixed release: DOWNGRADE to a release before 2.1 (Debian / Ubuntu)

apt-cache madison picotcp-ng sudo apt install picotcp-ng=<VERSION_BEFORE_2.1> sudo apt-mark hold picotcp-ng

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list picotcp-ng sudo dnf downgrade picotcp-ng-<VERSION_BEFORE_2.1> sudo dnf versionlock add picotcp-ng

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-33304?

picotcp: downgrade or apply the listed mitigation; picotcp-ng: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-33304 being exploited?

CVE-2021-33304 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-33304 affect?

CVE-2021-33304 affects picotcp, picotcp-ng. Severity is critical (CVSS 9.8). Double Free vulnerability in virtualsquare picoTCP v1.7.0 and picoTCP-NG v2.1 in modules/pico_fragments.c in function pico_fragments_reassemble, allows attackers to execute arbitrary code.

How urgent is CVE-2021-33304?

Priority 54/100. Critical severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2023-35849 HIGH 7.5 UPGRADE VirtualSquare picoTCP (aka PicoTCP-NG) through 2.1 does not properly check whether header sizes would result i
CVE-2023-35848 HIGH 7.5 UPGRADE VirtualSquare picoTCP (aka PicoTCP-NG) through 2.1 lacks certain size calculations before attempting to set a
CVE-2023-35847 HIGH 7.5 UPGRADE VirtualSquare picoTCP (aka PicoTCP-NG) through 2.1 does not have an MSS lower bound (e.g., it could be zero).
CVE-2023-35846 HIGH 7.5 UPGRADE VirtualSquare picoTCP (aka PicoTCP-NG) through 2.1 does not check the transport layer length in a frame before
CVE-2023-30463 HIGH 7.5 UPGRADE Altran picoTCP through 1.7.0 allows memory corruption (and subsequent denial of service) because of an integer

References

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