VulnerabilityAwaiting Analysis

CVE-2026-45100

Versions 3.4.0-beta through 3.6.5 and 4.0.0-beta contain a buffer overflow in the {s.b64encode} string transformation.

CRITICAL 9.1EPSS 0.83%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.83%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

Description

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 3.1: 9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
EPSS: 0.83% probability · 57th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-120
Source: security-advisories@github.com

EPSS trend

EPSS 0.8% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.