CVE-2026-82608 Overview
CVE-2026-82608 is an out-of-bounds read vulnerability in Kamailio, an open-source SIP server widely deployed in VoIP and IMS (IP Multimedia Subsystem) infrastructure. The flaw affects the get_4bytes function in src/modules/ims_registrar_scscf/cxdx_avp.c within the AVP (Attribute-Value Pair) Handler component. Kamailio versions up to 5.5.0 and 6.0.7 are impacted. A remote attacker with low privileges can trigger the condition, and the exploit has been publicly disclosed. The vendor notes that version 5.5.0 is end-of-life and no longer maintained. The issue is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
A remote, authenticated attacker can trigger an out-of-bounds read in the IMS S-CSCF registrar module, potentially leaking process memory or causing service instability.
Affected Products
- Kamailio SIP Server versions up to and including 5.5.0
- Kamailio SIP Server versions up to and including 6.0.7
- ims_registrar_scscf module (AVP Handler component)
Discovery Timeline
- 2026-08-31 - CVE-2026-82608 published to NVD
- 2026-08-31 - Last updated in NVD database
Technical Details for CVE-2026-82608
Vulnerability Analysis
The vulnerability resides in the ims_registrar_scscf module, which implements Serving Call Session Control Function (S-CSCF) registrar behavior for IMS deployments. The get_4bytes function reads four bytes from a buffer returned by cxdx_get_avp, which retrieves the AVP_Result_Code from a Diameter Cx/Dx interface message. The pre-patch code checked only whether the string pointer was non-null. It did not verify that the buffer length was at least four bytes before invoking get_4bytes. When a malformed AVP with fewer than four bytes of payload is processed, the function reads past the end of the allocated buffer.
Root Cause
The root cause is a missing length check on attacker-influenced input before a fixed-size read. The AVP payload length is not validated against the expected size of a 32-bit integer. This is a classic [CWE-119] boundary condition error where structural assumptions about protocol data are not enforced by validation logic.
Attack Vector
Exploitation occurs over the network by delivering a crafted Diameter message containing a truncated AVP_Result_Code value to a vulnerable S-CSCF instance. The attacker requires low privileges consistent with a peer able to send Cx/Dx signaling. Successful triggering results in an out-of-bounds read that may disclose adjacent process memory or destabilize the Kamailio process handling registrar traffic.
// Patch from src/modules/ims_registrar_scscf/cxdx_avp.c
// ims_registrar_scscf: check len before get_4bytes()
{
str s;
s = cxdx_get_avp(msg, AVP_Result_Code, 0, __FUNCTION__);
- if(!s.s)
+ if(!s.s || s.len < 4)
return 0;
*data = get_4bytes(s.s);
return 1;
Source: GitHub Commit abb5d60. The fix adds an explicit s.len < 4 check so that get_4bytes is only called when at least four bytes are available.
Detection Methods for CVE-2026-82608
Indicators of Compromise
- Unexpected crashes or restarts of the Kamailio process handling S-CSCF registrar traffic.
- Diameter Cx/Dx messages containing AVP_Result_Code payloads shorter than four bytes.
- Anomalous memory-region reads or segmentation faults logged by the host operating system for the kamailio binary.
Detection Strategies
- Inspect Diameter traffic for malformed AVP length fields, particularly Result-Code AVPs with truncated payloads.
- Compare running Kamailio binary versions against 5.5.0 and 6.0.7 to identify vulnerable hosts.
- Correlate SIP registrar failures with inbound Diameter peer activity to surface exploitation attempts.
Monitoring Recommendations
- Enable verbose logging on the ims_registrar_scscf module and forward logs to a centralized analytics platform for review.
- Monitor process telemetry for the kamailio service for crash loops or abnormal memory access patterns.
- Track Diameter peer connections and alert on new or unauthorized peers establishing Cx/Dx sessions.
How to Mitigate CVE-2026-82608
Immediate Actions Required
- Upgrade Kamailio to a version that includes commit abb5d60af6eefbd367bf6588c5589566b090e272 or later.
- Retire Kamailio 5.5.0 instances, as the vendor confirms this branch is no longer maintained.
- Restrict Diameter Cx/Dx peers to trusted, authenticated IMS elements only.
Patch Information
The upstream fix is available in the Kamailio commit abb5d60 and merged via Pull Request #4823. The tracking issue is Kamailio Issue #4816. Additional vulnerability metadata is available at VulDB CVE-2026-82608. Operators running 6.0.x should update to a build that includes this commit; operators on 5.5.0 should migrate to a supported release line.
Workarounds
- Disable the ims_registrar_scscf module if S-CSCF functionality is not required by the deployment.
- Enforce network-level ACLs to permit Diameter connections only from validated IMS peers.
- Deploy an intermediate Diameter proxy that validates AVP length fields before forwarding messages to Kamailio.
# Example: restrict Diameter Cx/Dx (TCP/3868) to trusted HSS peers only
iptables -A INPUT -p tcp --dport 3868 -s <trusted_hss_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 3868 -j DROP
# Verify installed Kamailio version
kamailio -v
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
