CVE-2021-35525Network attack vector

Subprocess hang via oversized Postfix request

Published Jun 28, 2021 · Updated Aug 4, 2024

Denial of service in PostSRSd before 1.11 allows remote attackers to hang a subprocess via an overly long request from Postfix. The Postfix-facing subprocess uses one bidirectional standard-I/O stream for reads and writes, and bytes left after an oversized GET line confuse its buffered I/O. Triggering requires Postfix to pass a malformed single query containing concatenated addresses; the maintainer did not establish a reliable external trigger, and the consequence is a hung subprocess.

CVSS severity5.3
Medium
EPSS probability1.62%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in PostSRSd before 1.11 allows remote attackers to hang a subprocess via an overly long request from Postfix. The Postfix-facing subprocess uses one bidirectional standard-I/O stream for reads and writes, and bytes left after an oversized GET line confuse its buffered I/O. Triggering requires Postfix to pass a malformed single query containing concatenated addresses; the maintainer did not establish a reliable external trigger, and the consequence is a hung subprocess.

The record

CVE
CVE-2021-35525
Published
Jun 28, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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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