FastStone Image Viewer up to 8.3 1bpp RLE Decoder out-of-bounds write

CVSS Meta Temp Score
CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.
Current Exploit Price (≈)
Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.
CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
5.7$0-$5k1.99-

Summaryinfo

A vulnerability classified as critical was found in FastStone Image Viewer up to 8.3. This affects an unknown function of the component 1bpp RLE Decoder. The manipulation results in out-of-bounds write. This vulnerability is reported as CVE-2026-101203. The attack can be launched remotely. Moreover, an exploit is present. The vendor was contacted early about this disclosure but did not respond in any way.

Detailsinfo

A vulnerability classified as critical has been found in FastStone Image Viewer up to 8.3. Affected is an unknown function of the component 1bpp RLE Decoder. The manipulation with an unknown input leads to a out-of-bounds write vulnerability. CWE is classifying the issue as CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. This is going to have an impact on confidentiality, integrity, and availability.

This vulnerability is traded as CVE-2026-101203. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. Technical details are unknown but an exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/28/2026).

It is declared as proof-of-concept. The vendor was contacted early about this disclosure but did not respond in any way.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

Name

Version

License

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.3
VulDB Meta Temp Score: 5.7

VulDB Base Score: 6.3
VulDB Temp Score: 5.7
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Out-of-bounds write
CWE: CWE-787 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Proof-of-Concept
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

09/28/2026 Advisory disclosed
09/28/2026 +0 days VulDB entry created
09/28/2026 +0 days VulDB entry last update

Sourcesinfo

Status: Not defined

CVE: CVE-2026-101203 (🔒)
GCVE (CVE): GCVE-0-2026-101203
GCVE (VulDB): GCVE-100-411012
scip Labs: https://www.scip.ch/en/?labs.20161013

Entryinfo

Created: 09/28/2026 11:45
Changes: 09/28/2026 11:45 (51)
Complete: 🔍
Submitter: jonzab
Cache ID: 216::103

Submitinfo

Accepted

  • Submit #907575: FastStone Soft FastStone Image Viewer 8.3 Heap-based buffer overflow (out-of-bounds write) (by jonzab)

Once again VulDB remains the best source for vulnerability data.

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