# CVE-2026-121508: µD3TN BPv6 fragmenter use-after-free in cleanup

Source: https://junglewise.ai/threats/cve-2026-121508-use-after-free-in-d3tn-bpv6-fragmenter-cleanup-allows  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-03. Updated: 2026-11-03  
License: CC BY 4.0 with a link back

CVE-2026-121508 · Severity: medium · CVSS 5.9 · Published 2026-11-03

µD3TN is a delay-tolerant networking daemon used in space and challenged-network communications. A use-after-free bug in the BPv6 fragmenter can crash the daemon when fragmentation fails due to memory allocation problems, disrupting all bundle routing on that node. An unauthenticated attacker can trigger this via a malformed network message or through the AAP 2.0 control interface.

Technologies: [D3TN µD3TN](https://junglewise.ai/threats/technologies/d3tn). Vendors: [D3TN](https://junglewise.ai/threats/vendors/d3tn).

## Quick answers

**Is CVE-2026-121508 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-121508 being exploited in the wild.

**How severe is CVE-2026-121508?** Medium severity, with a CVSS score of 5.9, published 3 November 2026.

**Which products and versions are affected?** D3TN µD3TN.

**Is there a fix for CVE-2026-121508?** No fixed version is recorded yet. Restrict access to the AAP 2.0 dispatcher control interface to trusted hosts. Limit incoming BPv6 bundles to trusted peers or networks to reduce exposure to malformed fragmentation requests. 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-2026-121508 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-121508?** Check whether you run D3TN µD3TN. 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


Restrict access to the AAP 2.0 dispatcher control interface to trusted hosts. Limit incoming BPv6 bundles to trusted peers or networks to reduce exposure to malformed fragmentation requests.

## Technical details

A use-after-free and double-free vulnerability exists in the BPv6 fragmenter cleanup logic in components/bundle6/fragment.c. When a block duplication fails during fragmentation, the cleanup attempts to restore the payload entry by writing through a cursor that has already advanced past it, forming a cycle in the block list. bundle_free then traverses this cycle and frees the same node twice. The attack requires a specially crafted BPv6 bundle with a payload block followed by a MUST_BE_REPLICATED block, combined with an allocation failure during fragmentation.

## Affected products

- D3TN µD3TN

## Timeline

- 2026-11-03: disclosed

## References

- [https://gitlab.com/d3tn/ud3tn/-/work_items/291](https://gitlab.com/d3tn/ud3tn/-/work_items/291)

## Related threats

- [µD3TN SPP parser off-by-one heap overflow](https://junglewise.ai/threats/cve-2026-121513-off-by-one-heap-overflow-in-d3tn-v0-15-1-spp-parser-allows)
- [µD3TN memory leak with amplification in BPv6 EID reference handling](https://junglewise.ai/threats/cve-2026-121512-memory-leak-with-amplification-in-d3tn-bpv6-eid-reference)
- [µD3TN BPv6/BPv7 Fragmenter heap buffer out-of-bounds read](https://junglewise.ai/threats/cve-2026-121511-heap-out-of-bounds-read-in-d3tn-bpv6-bpv7-fragmenter-allows)
- [µD3TN BPv6 heap out-of-bounds write in administrative record parser](https://junglewise.ai/threats/cve-2026-121510-remote-unauthenticated-heap-out-of-bounds-write-in-d3tn-bpv6)
- [µD3TN BPv6 fragmenter double free in block duplication](https://junglewise.ai/threats/cve-2026-121507-double-free-in-d3tn-bpv6-fragmenter-block-duplication-allows)