CVE-2021-32686Network attack vector

TLS server crash via SSL socket races

Published Jul 23, 2021 · Updated Nov 4, 2025

Race conditions in the SSL socket server in PJSIP PJPROJECT before 2.11.1 allow remote attackers to crash TLS servers. The accepted active socket is created without its group lock, while the parent listener can be destroyed during a handshake and verify_cb relies on an assertion rather than runtime validation. Triggering either lifetime race requires heavy concurrent incoming TLS connections; client applications are generally unaffected unless they accept such connections.

CVSS severity5.9
Medium
EPSS probability2.07%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race conditions in the SSL socket server in PJSIP PJPROJECT before 2.11.1 allow remote attackers to crash TLS servers. The accepted active socket is created without its group lock, while the parent listener can be destroyed during a handshake and verify_cb relies on an assertion rather than runtime validation. Triggering either lifetime race requires heavy concurrent incoming TLS connections; client applications are generally unaffected unless they accept such connections.

The record

CVE
CVE-2021-32686
Published
Jul 23, 2021
Updated
Nov 4, 2025
Vendor
PJSIP
Product
PJPROJECT
Classifications
CWE-362, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 2025Record 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=< 2.11.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PJSIP · PJPROJECTversion=< 2.11.1

Published CVSS scores

4.3NISTAV:N/AC:M/Au:N/C:N/I:N/A:P
5.9NISTCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

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-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499Endpoint Denial of Service

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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