CVE-2021-22925Public exploitNetwork attack vector

Stack disclosure via malformed TELNET environment option

Published Aug 5, 2021 · Updated Apr 16, 2026

Information disclosure in curl 7.7 through 7.77.0 allows remote attackers controlling a TELNET server to read stack data. The NEW_ENV option parser passes incorrectly parsed sscanf() output from an uninitialized stack buffer to the TELNET server. Exposure requires a vulnerable application or command invocation to set CURLOPT_TELNETOPTIONS or -t and connect over cleartext; integrity and availability are unaffected.

CVSS severity5.3
Medium
EPSS probability4.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Information disclosure in curl 7.7 through 7.77.0 allows remote attackers controlling a TELNET server to read stack data. The NEW_ENV option parser passes incorrectly parsed sscanf() output from an uninitialized stack buffer to the TELNET server. Exposure requires a vulnerable application or command invocation to set CURLOPT_TELNETOPTIONS or -t and connect over cleartext; integrity and availability are unaffected.

The record

CVE
CVE-2021-22925
Published
Aug 5, 2021
Updated
Apr 16, 2026
Vendor
curl
Product
curl
Classifications
CWE-200, CWE-908, CWE-457, T1048.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=curl 7.7 to and including 7.77.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=curl 7.7 to and including 7.77.0

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
CWE-908Use of Uninitialized Resource
CWE-457Use of Uninitialized Variable
T1048.003Exfiltration Over Unencrypted Non-C2 Protocol

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo