CVE-2021-22898Public exploitNetwork attack vector

Stack disclosure via unchecked TELNET option parsing

Published Jun 11, 2021 · Updated Apr 16, 2026

Information disclosure in curl 7.7 through 7.76.1 allows attackers to receive stack data through a malformed TELNET NEW_ENV option. The TELNET option parser mishandles the return from sscanf when a value exceeds 127 bytes, leaving part of a 2,048-byte send buffer uninitialized. A user or calling application must supply the oversized value and connect to a TELNET server, which receives about 1,800 noncontiguous stack bytes over cleartext.

CVSS severity3.1
Low
EPSS probability4.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in curl 7.7 through 7.76.1 allows attackers to receive stack data through a malformed TELNET NEW_ENV option. The TELNET option parser mishandles the return from sscanf when a value exceeds 127 bytes, leaving part of a 2,048-byte send buffer uninitialized. A user or calling application must supply the oversized value and connect to a TELNET server, which receives about 1,800 noncontiguous stack bytes over cleartext.

The record

CVE
CVE-2021-22898
Published
Jun 11, 2021
Updated
Apr 16, 2026
Vendor
curl
Product
curl
Classifications
CWE-200, CWE-909, CWE-457
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 11, 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

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Is a vulnerable build present?

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

  1. Affected versionversion=7.7 through 7.76.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=7.7 through 7.76.1

Published CVSS scores

2.6NIST NVDAV:N/AC:H/Au:N/C:P/I:N/A:N
3.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
3.1CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/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.

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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 exploitPublished

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
CWE-909Missing Initialization of Resource
CWE-457Use of Uninitialized Variable

Public exploit references

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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