CVE-2021-21375Public exploitNetwork attack vector

Process crash via failed SDP renegotiation

Published Mar 10, 2021 · Updated Aug 3, 2024

Denial of service in PJSIP PJPROJECT 2.10 and earlier allows remote attackers to crash a SIP application through crafted 183 responses. The pjmedia_sdp_neg_modify_local_offer2 function reuses a null active_local_sdp after an earlier SDP negotiation fails, and pj_strdup dereferences that null source while a later answer is processed. Exploitation requires a victim-initiated INVITE and two 183 responses; the first must fail SDP negotiation, after which the second terminates the affected process.

CVSS severity6.5
Medium
EPSS probability2.08%
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 PJSIP PJPROJECT 2.10 and earlier allows remote attackers to crash a SIP application through crafted 183 responses. The pjmedia_sdp_neg_modify_local_offer2 function reuses a null active_local_sdp after an earlier SDP negotiation fails, and pj_strdup dereferences that null source while a later answer is processed. Exploitation requires a victim-initiated INVITE and two 183 responses; the first must fail SDP negotiation, after which the second terminates the affected process.

The record

CVE
CVE-2021-21375
Published
Mar 10, 2021
Updated
Aug 3, 2024
Vendor
PJSIP
Product
PJPROJECT
Classifications
CWE-400, CWE-754, 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?

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

  1. Affected versionversion=<= 2.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PJSIP · PJPROJECTversion=<= 2.10

Published CVSS scores

4.3NISTAV:N/AC:M/Au:N/C:N/I:N/A:P
6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
CWE-754Improper Check for Unusual or Exceptional Conditions
T1499.004Application or System Exploitation

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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