CVE-2021-27918Network attack vector

Application hang via unhandled mid-element EOF

Published Mar 10, 2021 · Updated Aug 3, 2024

Infinite loop in Go encoding/xml 1.15.8 and earlier and 1.16.0 allows attackers to hang applications during XML decoding. Decoder.Token fails to convert EOF from a custom TokenReader while an element remains open into a terminal syntax error, so Decode, DecodeElement, or Skip continues looping. Reachability requires application code to use xml.NewTokenDecoder with a custom TokenReader whose attacker-influenced token stream ends inside an open element; the loop consumes processing capacity without reading or changing data.

CVSS severity7.5
High
EPSS probability2.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite loop in Go encoding/xml 1.15.8 and earlier and 1.16.0 allows attackers to hang applications during XML decoding. Decoder.Token fails to convert EOF from a custom TokenReader while an element remains open into a terminal syntax error, so Decode, DecodeElement, or Skip continues looping. Reachability requires application code to use xml.NewTokenDecoder with a custom TokenReader whose attacker-influenced token stream ends inside an open element; the loop consumes processing capacity without reading or changing data.

The record

CVE
CVE-2021-27918
Published
Mar 10, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:P

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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