CVE-2021-37706Network attack vector

Code execution via STUN attribute length underflow

Published Dec 22, 2021 · Updated Nov 4, 2025

Integer underflow in PJPROJECT 2.11.1 and earlier allows remote attackers to execute code via a crafted UDP STUN ERROR-CODE attribute. decode_errcode_attr() subtracts four from the unvalidated attribute length, then passes the negative string length to pj_strdup() while copying the reason phrase. The target must use STUN and accept the forged datagram from an attacker with network reachability; successful exploitation executes code on the target.

CVSS severity7.3
High
EPSS probability4.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer underflow in PJPROJECT 2.11.1 and earlier allows remote attackers to execute code via a crafted UDP STUN ERROR-CODE attribute. decode_errcode_attr() subtracts four from the unvalidated attribute length, then passes the negative string length to pj_strdup() while copying the reason phrase. The target must use STUN and accept the forged datagram from an attacker with network reachability; successful exploitation executes code on the target.

The record

CVE
CVE-2021-37706
Published
Dec 22, 2021
Updated
Nov 4, 2025
Vendor
PJSIP
Product
PJPROJECT
Classifications
CWE-191, T1210
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 22, 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

7.3GitHub CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

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-191Integer Underflow (Wrap or Wraparound)
T1210Exploitation of Remote Services

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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