CVE-2021-28903Network attack vector

Remote service crash via uncontrolled XML recursion

Published May 20, 2021 · Updated Aug 3, 2024

Uncontrolled recursion in CESNET libyang 1.0.225 and earlier allows remote attackers to crash a consuming service with nested XML. lyxml_parse_mem() passes nested elements to lyxml_parse_elem(), which recurses without an effective depth limit until the process stack is exhausted. Reachability requires an application to parse attacker-controlled XML with the affected library; exploitation terminates that process without reported data disclosure or modification.

CVSS severity7.5
High
EPSS probability2.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled recursion in CESNET libyang 1.0.225 and earlier allows remote attackers to crash a consuming service with nested XML. lyxml_parse_mem() passes nested elements to lyxml_parse_elem(), which recurses without an effective depth limit until the process stack is exhausted. Reachability requires an application to parse attacker-controlled XML with the affected library; exploitation terminates that process without reported data disclosure or modification.

The record

CVE
CVE-2021-28903
Published
May 20, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-674, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 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 NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV: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.

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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