CVE-2026-45100

OpenSIPS is a Session Initiation Protocol (SIP) server implementation. Versions 3.4.0-beta through 3.6.5 and 4.0.0-beta contain a buffer overflow in the {s.b64encode} string transformation. The size check for {s.b64encode} only verifies that the input fits within the 64 KB transformation buffer, but base64 encoding expands the data by roughly a third, so an input between about 49,153 and 65,535 bytes produces more output than the buffer can hold and overflows it by up to 21,844 bytes. Because these transformation buffers sit next to each other in memory and are reused for chained transformations, the overflow writes attacker-controlled data into the adjacent buffer and corrupts values used by later transformations processing the same SIP message. A remote attacker can trigger this by sending a SIP message with a large header value (roughly 50,000 bytes or more) when the routing script applies {s.b64encode} to attacker-controlled input, making exploitability dependent on the deployment's routing configuration. This issue has been fixed in versions 3.6.6 and 4.0.0-rc1.

CVSS v3 9.1 CRITICAL

9.1^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/OpenSIPS/opensips/commit/4d23613b65579b073784a07a65d3bf52443a4efb
https://github.com/OpenSIPS/opensips/commit/5f103effaf5f372cccffe0b138f16998eba12668
https://github.com/OpenSIPS/opensips/security/advisories/GHSA-35fr-6rv9-vp68
https://github.com/OpenSIPS/opensips/security/advisories/GHSA-35fr-6rv9-vp68

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-04 22:17

Updated : 2026-09-08 20:41

NVD link : CVE-2026-45100

Mitre link : CVE-2026-45100

CVE.ORG link : CVE-2026-45100

JSON object : View

Products Affected

No product.

CWE

CWE-120

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

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