CVE-2018-15853 (published 2018-08-25T21:29Z)

Endless recursion exists in xkbcomp/expr.c in xkbcommon and libxkbcommon before 0.8.1, which could be used by local attackers to crash xkbcommon users by supplying a crafted keymap file that triggers boolean negation.

Severity: LOW
CVSS v2 base score: 2.1 (AV:L/AC:L/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 5.5, MEDIUM (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-400
cwe_name: Uncontrolled Resource Consumption
description: The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
extended_description: 
            Limited resources include memory, file system storage, database connection pool entries, and CPU. If an attacker can trigger the allocation of these limited resources, but the number or size of the resources is not controlled, then the attacker could cause a denial of service that consumes all available resources. This would prevent valid users from accessing the product, and it could potentially have an impact on the surrounding environment. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system.
            There are at least three distinct scenarios which can commonly lead to resource exhaustion:
               
                  Lack of throttling for the number of allocated resources
                  Losing all references to a resource before reaching the shutdown stage
                  Not closing/returning a resource after processing
               
            Resource exhaustion problems are often result due to an incorrect implementation of the following situations:
               
                  Error conditions and other exceptional circumstances.
                  Confusion over which part of the program is responsible for releasing the resource.
               
         
         

Fix information:
repo_url: https://github.com/xkbcommon/libxkbcommon
commit_details: repo_url: https://github.com/xkbcommon/libxkbcommon
author: Ran Benita
author_date: 2018-03-10 23:10:47+02:00
msg: xkbcomp: fix stack overflow when evaluating boolean negation

The expression evaluator would go into an infinite recursion when
evaluating something like this as a boolean: `!True`. Instead of
recursing to just `True` and negating, it recursed to `!True` itself
again.

Bug inherited from xkbcomp.

Caught with the afl fuzzer.

Signed-off-by: Ran Benita <ran234@gmail.com>
repository: repo_url: https://github.com/xkbcommon/libxkbcommon
repo_name: xkbcommon/libxkbcommon
description: keymap handling library for toolkits and window systems
repo_language: C
owner: xkbcommon
file_changes: filename: expr.c
change_type: ModificationType.MODIFY
diff: @@ -165,7 +165,7 @@ ExprResolveBoolean(struct xkb_context *ctx, const ExprDef *expr,
 
     case EXPR_INVERT:
     case EXPR_NOT:
-        ok = ExprResolveBoolean(ctx, expr, set_rtrn);
+        ok = ExprResolveBoolean(ctx, expr->unary.child, set_rtrn);
         if (ok)
             *set_rtrn = !*set_rtrn;
         return ok;

programming_language: C