CVE-2020-27507Public exploitNetwork attack vector

Unauthenticated server crash via malformed INVITE rebuilding

Published Mar 15, 2023 · Updated Feb 27, 2025

Buffer overflow in Kamailio SIP Server before 5.5.0 allows remote attackers to crash the service with a malformed INVITE request. The tm module's build_local_reparse() function copies duplicate CSeq, From, To, or Call-ID headers while rebuilding a request; an overlength tag then causes writes beyond the allocated buffer. No authentication or user interaction is required, and sending the crafted SIP request to a reachable listener terminates the server and interrupts call processing.

CVSS severity9.8
Critical
EPSS probability1.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Buffer overflow in Kamailio SIP Server before 5.5.0 allows remote attackers to crash the service with a malformed INVITE request. The tm module's build_local_reparse() function copies duplicate CSeq, From, To, or Call-ID headers while rebuilding a request; an overlength tag then causes writes beyond the allocated buffer. No authentication or user interaction is required, and sending the crafted SIP request to a reachable listener terminates the server and interrupts call processing.

The record

CVE
CVE-2020-27507
Published
Mar 15, 2023
Updated
Feb 27, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 15, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 27, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

9.8NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo