CVE-2004-0640: Format string vulnerability in the SSL_set_verify function in telnetd.c for SSLtelnet daemon (SSLtelnetd) 0.13

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HIGH 10.0WATCHLISTDOWNGRADEDOWNGRADE

CVE-2004-0640 is a high-severity flaw (CVSS 10.0) affecting linux netkit, secure telnet. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Format string vulnerability in the SSL_set_verify function in telnetd.c for SSLtelnet daemon (SSLtelnetd) 0.13 allows remote attackers to execute arbitrary code.

Why this priority

Critical severity
EPSS top 9%: very likely to be exploited
On your watchlist

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

Risk facts

CVSS score	10.0 (High)
EPSS exploit chance	4.5% (top 9%)
CISA exploited list	No
Published	2004-08-06
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: netkit · ssltelnetd

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2004-08-06 04:00 UTCPublished CVE record published
2026-06-16 22:06 UTCUpdated Record last modified

netkit linux netkit DOWNGRADE

Affected: 0.17 · 0.17.17

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.17

1. Check installed version

apt-cache policy linux-netkit || rpm -q linux-netkit || linux-netkit --version

2. No fixed release: DOWNGRADE to a release before 0.17 (Debian / Ubuntu)

apt-cache madison linux-netkit sudo apt install linux-netkit=<VERSION_BEFORE_0.17> sudo apt-mark hold linux-netkit

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

dnf --showduplicates list linux-netkit sudo dnf downgrade linux-netkit-<VERSION_BEFORE_0.17> sudo dnf versionlock add linux-netkit

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.

ssltelnetd secure telnet DOWNGRADE

Affected: 0.13.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.13.1

1. Check installed version

apt-cache policy secure-telnet || rpm -q secure-telnet || secure-telnet --version

2. No fixed release: DOWNGRADE to a release before 0.13.1 (Debian / Ubuntu)

apt-cache madison secure-telnet sudo apt install secure-telnet=<VERSION_BEFORE_0.13.1> sudo apt-mark hold secure-telnet

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

dnf --showduplicates list secure-telnet sudo dnf downgrade secure-telnet-<VERSION_BEFORE_0.13.1> sudo dnf versionlock add secure-telnet

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-2004-0640?

linux netkit: downgrade or apply the listed mitigation; secure telnet: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2004-0640 being exploited?

CVE-2004-0640 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-2004-0640 affect?

CVE-2004-0640 affects linux netkit, secure telnet. Severity is high (CVSS 10.0). Format string vulnerability in the SSL_set_verify function in telnetd.c for SSLtelnet daemon (SSLtelnetd) 0.13 allows remote attackers to execute arbitrary code.

How urgent is CVE-2004-0640?

Priority 63/100. Critical severity; EPSS top 9%: very likely to be exploited; On your watchlist

Related CVEs

CVE-2005-0178 MEDIUM 6.2 DOWNGRADE DOWNGRADE Race condition in the setsid function in Linux before 2.6.8.1 allows local users to cause a denial of service
CVE-2001-0554 HIGH 10.0 DOWNGRADE DOWNGRADE Buffer overflow in BSD-based telnetd telnet daemon on various operating systems allows remote attackers to exe

References

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