Vikunja before 2.6.0 Denial of Service via Decompression Bomb

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Vikunja before 2.6.0 fails to limit archive expansion during data import, allowing authenticated users to cause denial of service. Attackers can upload highly compressed files that expand to tens of gigabytes in memory and disk, exhausting server resources and crashing the instance.

Source published

15 Sep 2026 15:18:24 UTC

Source modified

17 Sep 2026 19:28:09 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS 4.0 · 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Vikunja before 2.6.0 fails to limit archive expansion during data import, allowing authenticated users to cause denial of service. Attackers can upload highly compressed files that expand to tens of gigabytes in memory and disk, exhausting server resources and crashing the instance.

Source published

Sep 15, 2026, 3:18:24 PM (timezone not stated)

Source modified

Sep 17, 2026, 7:28:09 PM (timezone not stated)

Observed here

7 Nov 2026 15:25:01 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Vikunja before 2.6.0 fails to limit archive expansion during data import, allowing authenticated users to cause denial of service. Attackers can upload highly compressed files that expand to tens of gigabytes in memory and disk, exhausting server resources and crashing the instance.

Source published

15 Sep 2026 16:17:54 UTC

Source modified

17 Sep 2026 20:18:54 UTC

Observed here

25 Oct 2026 16:19:22 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

### Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-w7jp-mf2v-8342. This link is maintained to preserve external references. ### Original Description Vikunja before 2.6.0 fails to limit archive expansion during data import, allowing authenticated users to cause denial of service. Attackers can upload highly compressed files that expand to tens of gigabytes in memory and disk, exhausting server resources and crashing the instance.

Source published

15 Sep 2026 18:32:30 UTC

Source modified

9 Oct 2026 21:00:07 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Publisher rating · HIGH

### Summary Vikunja lets you export your data as a zip and import it back. The import doesn't limit how large the archive expands to, how many files it contains, or how much storage one user can consume, and it appears to hold the whole archive in memory while processing it. Because the archive is compressed, a ~20 MB upload made of highly compressible content expands to tens of gigabytes once imported. A single crafted upload is enough to exhaust the server's memory or fill its disk and knock the whole instance offline. It can be repeated or run in parallel, since nothing stops a user from starting several imports at once. ### Details The import accepts an archive in the same layout the built-in export produces: a manifest describing projects and tasks, plus the attachment files those tasks reference. Each individual file inside the archive is size-checked, but there's no ceiling on the total uncompressed size or on the number of files, and there's no per-user storage quota anywhere. On top of that, the server seems to buffer every attachment in memory before writing it out, so the peak memory cost is the sum of all decompressed files at once, not one at a time. Compression is the key factor: a file full of a repeating byte (e.g. zeroes) shrinks by roughly a thousand to one. So an archive that fits under the upload size limit (around 20 MB) can describe on the order of a thousand ~20 MB attachments, which the server then expands to tens of gigabytes in RAM and writes to disk. When memory runs out the process is killed; when the disk fills, the instance (and anything else on that host) stops working. Nothing serialises imports, so a user can also fire several in parallel to reach the limit faster. The fix is to cap the total uncompressed size and the file count per archive, stream each file to disk instead of buffering them all in memory, enforce a per-user storage quota, and refuse a new import while one is already running for that user. ### PoC The attacker needs an ordinary account that can use the import feature. 1. Build a zip in the export format containing one project with for example ~200 tasks, each referencing an attachment, and ~200 attachment files, each 18 MB of zero bytes. Filled with zeroes, the whole thing compresses to roughly 4 MB (under the upload limit). ```python #!/usr/bin/env python3 import argparse, json, os, zipfile CHUNK = b"\0" * (1024 * 1024) def build(out, n, size, version): tasks = [{"title": f"t{i}", "attachments": [{"file": {"id": i, "name": "a"}}]} for i in range(1, n + 1)] data = json.dumps([{"title": "bomb", "tasks": tasks, "child_projects": []}]).encode() with zipfile.ZipFile(out, "w", zipfile.ZIP_DEFLATED, compresslevel=9) as z: z.writestr("VERSION", version) z.writestr("data.json", data) for i in range(1, n + 1): with z.open(f"files/{i}", "w") as f: for _ in range(size): f.write(CHUNK) raw = n * size * 1024**2 print(f"[+] {out}: {os.path.getsize(out)/1024**2:.2f} MiB " f"({raw/1024**3:.1f} GiB uncompressed)") p = argparse.ArgumentParser() p.add_argument("-o", "--out", default="bomb.zip") p.add_argument("-n", "--files", type=int, default=200) p.add_argument("-s", "--size-mib", type=int, default=18) p.add_argument("--version", default="v2.5.0") a = p.parse_args() build(a.out, a.files, a.size_mib, a.version) ``` 3. Upload it to the import endpoint: ``` PUT /api/v1/migration/vikunja-file/migrate (multipart file upload: the crafted zip) ``` 4. Watch the server. Memory climbs into 3.5 GB within seconds and the disk fills with the expanded files. On a typical host the process is OOM-killed or the disk fills, and the instance stops responding for everyone. Repeat, or send several uploads at once, to reach the limit reliably. (You can derive the exact archive layout in step 1 by first exporting your own data once and inspecting the zip it hands back.) ### Impact Denial of service (availability). One authenticated user, with a single upload, can drive the server into tens of GB of memory and disk usage, killing the process or filling the disk. This takes the whole instance down for every user, and if the disk is shared with other services on the host, those go down too. No admin rights and no victim interaction are required, any account that can import data is enough. Recovery needs an operator to reclaim memory/disk and clear the partially written import.

Source published

9 Oct 2026 20:52:52 UTC

Source modified

19 Oct 2026 21:40:53 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH

Vikunja: Denial of service via decompression bomb in the data import in code.vikunja.io/api. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: code.vikunja.io/api before v2.6.0.

Source published

19 Oct 2026 21:08:26 UTC

Source modified

19 Oct 2026 21:31:37 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.