CVE-2021-47764: AbsoluteTelnet 11.24 contains a denial of service vulnerability that allows local attackers to crash the appli

Routine

MEDIUM 5.5DOWNGRADE

CVE-2021-47764 is a medium-severity flaw (CVSS 5.5) affecting absolutetelnet. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

AbsoluteTelnet 11.24 contains a denial of service vulnerability that allows local attackers to crash the application by manipulating DialUp connection and license name fields. Attackers can generate a 1000-character payload and paste it into specific input fields to trigger application crashes and force unexpected termination.

Why this priority

Public exploit reference

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

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 91%)
CISA exploited list	No
Weakness	CWE-787
Published	2026-01-15
Last modified	2026-06-17

Publisher (CNA): VulnCheck · Vendor: celestialsoftware

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

Am I affected?

Timeline

2026-01-15 16:16 UTCPublished CVE record published
2026-06-17 04:18 UTCUpdated Record last modified

celestialsoftware absolutetelnet DOWNGRADE

Affected: 11.24

Fixed in: no fixed release known

Safe to downgrade to: a release before 11.24

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 11.24 (Debian / Ubuntu)

apt-cache madison absolutetelnet sudo apt install absolutetelnet=<VERSION_BEFORE_11.24> sudo apt-mark hold absolutetelnet

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

dnf --showduplicates list absolutetelnet sudo dnf downgrade absolutetelnet-<VERSION_BEFORE_11.24> sudo dnf versionlock add absolutetelnet

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-2021-47764?

absolutetelnet: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-47764 being exploited?

CVE-2021-47764 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-2021-47764 affect?

CVE-2021-47764 affects absolutetelnet. Severity is medium (CVSS 5.5). AbsoluteTelnet 11.24 contains a denial of service vulnerability that allows local attackers to crash the application by manipulating DialUp connection and license name fields. Attackers can generate a 1000-character payload and paste it int

How urgent is CVE-2021-47764?

Priority 27/100. Public exploit reference

Related CVEs

CVE-2021-47765 MEDIUM 5.5 DOWNGRADE AbsoluteTelnet 11.24 contains a denial of service vulnerability that allows local attackers to crash the appli
CVE-2020-37166 MEDIUM 6.2 DOWNGRADE AbsoluteTelnet 11.12 contains a denial of service vulnerability in the SSH2 username input field that allows l
CVE-2020-37165 MEDIUM 6.2 UPGRADE AbsoluteTelnet 11.12 contains a denial of service vulnerability that allows local attackers to crash the appli
CVE-2020-37164 MEDIUM 6.2 UPGRADE AbsoluteTelnet 11.12 contains a denial of service vulnerability that allows local attackers to crash the appli

References

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