OpenSIPS: Buffer Overflow in Base64 Encode Transformation

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-45100
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-04 22:17:14 UTC
Updated2026-08-05 15:16:47 UTC
DescriptionOpenSIPS 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.

Risk And Classification

Primary CVSS: v3.1 9.1 CRITICAL from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Problem Types: CWE-120 | CWE-120 CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
3.1CNADECLARED9.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA OpenSIPS Opensips affected >= 3.4.0-beta, < 3.6.6 Not specified
CNA OpenSIPS Opensips affected >= 4.0.0-beta, < 4.0.0-rc1 Not specified

References

ReferenceSourceLinkTags
github.com/OpenSIPS/opensips/commit/4d23613b65579b073784a07a65d3bf52443a... [email protected] github.com
github.com/OpenSIPS/opensips/commit/5f103effaf5f372cccffe0b138f16998eba1... [email protected] github.com
github.com/OpenSIPS/opensips/security/advisories/GHSA-35fr-6rv9-vp68 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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