# CVE-2026-121943: Irontec sngrep out-of-bounds stack read in SIP parser

Source: https://junglewise.ai/threats/cve-2026-121943-irontec-sngrep-through-1-9-0-contains-an-out-of-bounds-stack  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-04. Updated: 2026-11-04  
License: CC BY 4.0 with a link back

CVE-2026-121943 · Severity: medium · CVSS 4.8 · Published 2026-11-04

Irontec sngrep is a SIP packet capture and analysis tool used to monitor VoIP communications. A malformed SIP packet of exactly 10240 bytes can cause the application to crash or leak sensitive memory contents from the server's stack into packet display fields. An attacker can exploit this remotely by sending a crafted SIP packet or providing a malicious packet capture file.

Technologies: [Irontec Sngrep](https://junglewise.ai/threats/technologies/sngrep). Vendors: [Irontec](https://junglewise.ai/threats/vendors/irontec).

## Quick answers

**Is CVE-2026-121943 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-121943 being exploited in the wild.

**How severe is CVE-2026-121943?** Medium severity, with a CVSS score of 4.8, published 4 November 2026.

**Which products and versions are affected?** Irontec Sngrep through 1.9.0.

**Is there a fix for CVE-2026-121943?** No fixed version is recorded yet. Disable live SIP packet capture if the source is untrusted; process only pcap files from verified sources until a patched version is deployed. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-121943 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-121943?** Check whether you run Irontec Sngrep at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix


Disable live SIP packet capture if the source is untrusted; process only pcap files from verified sources until a patched version is deployed.

## Technical details

An off-by-one error in the length check of sip_check_packet and sip_validate_packet functions allows a SIP payload of exactly 10240 bytes (MAX_SIP_PAYLOAD) to be copied into a fixed-size stack buffer without a NUL terminator. When the buffer is later passed to regexec as a C string, it reads past the buffer boundary until finding a zero byte in adjacent stack memory, causing an out-of-bounds read. The vulnerability is reachable from untrusted network packets or pcap files with no prior authentication.

## Affected products

- Irontec sngrep through 1.9.0

## Timeline

- 2026-11-04: disclosed
- 2026-10-21: other: vulnerability reported to maintainers

## References

- [https://github.com/irontec/sngrep/blob/v1.9.0/src/sip.c](https://github.com/irontec/sngrep/blob/v1.9.0/src/sip.c)
- [https://github.com/irontec/sngrep/issues/589](https://github.com/irontec/sngrep/issues/589)

## Related threats

- [sngrep infinite loop in capture_packet_reasm_ip](https://junglewise.ai/threats/cve-2026-121944-sngrep-through-1-9-0-contains-an-infinite-loop-vulnerability-in)
- [sngrep stack buffer overflow in SIP header formatting](https://junglewise.ai/threats/cve-2026-90558-sngrep-stack-buffer-overflow-in-sip-header-formatting)