# CVE-2026-121507: µD3TN BPv6 fragmenter double free in block duplication

Source: https://junglewise.ai/threats/cve-2026-121507-double-free-in-d3tn-bpv6-fragmenter-block-duplication-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-2026-121507 · Severity: medium · CVSS 5.9 · Published 2026-11-03

µD3TN is a bundle protocol router used in delay-tolerant networks for reliable message delivery. A double-free memory corruption flaw in the BPv6 fragmenter can be triggered by an unauthenticated attacker sending a specially crafted bundle, causing the µD3TN process to crash and halt all message forwarding on the affected node.

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

## Quick answers

**Is CVE-2026-121507 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-121507 being exploited in the wild.

**How severe is CVE-2026-121507?** 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-2026-121507?** No fixed version is recorded yet. Clear the aliased data pointer immediately after the shallow copy in `bundle_block_dup` by setting `dup->data = NULL` before the EID reference list allocation loop to prevent the error path from freeing memory the duplicate does not own.</anigation>
<parameter name="timeline">[{"kind":"disclosed","at":"2026-11-03"}] 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-2026-121507 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-121507?** 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


Clear the aliased data pointer immediately after the shallow copy in `bundle_block_dup` by setting `dup->data = NULL` before the EID reference list allocation loop to prevent the error path from freeing memory the duplicate does not own.</anigation>
<parameter name="timeline">[{"kind":"disclosed","at":"2026-11-03"}]

## Technical details

The `bundle_block_dup` function performs a shallow copy before allocating a new data buffer for EID references, leaving a dangling pointer to the source block's buffer in the duplicate. If EID reference list allocation fails, the error path frees the source block's buffer through the duplicate, and the buffer is freed again when the source bundle is discarded. The vulnerability requires a received bundle with EID references that triggers fragmentation and an allocation failure during that fragmentation.

## Affected products

- D3TN µD3TN

## References

- [https://gitlab.com/d3tn/ud3tn/-/work_items/293](https://gitlab.com/d3tn/ud3tn/-/work_items/293)

## 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 use-after-free in cleanup](https://junglewise.ai/threats/cve-2026-121508-use-after-free-in-d3tn-bpv6-fragmenter-cleanup-allows)