Acrobat Reader: Time-of-check Time-of-use (TOCTOU) Race Condition
CVE-2024-39420 is a high-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in Acrobat Reader from Adobe, with a CVSS 3.1 base score of 7.0 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. Affected Acrobat Reader versions: 24.003.20054 and earlier; 20.005.30636 and earlier; 20.005.30635 and earlier. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 3.49% chance of exploitation within 30 days, higher than 89% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of Acrobat Reader you run against the affected versions below, and install the vendor's latest release.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Adobe | Acrobat Reader | 24.003.20054 and earlier; 20.005.30636 and earlier; 20.005.30635 and earlier | Not stated |
| Adobe | acrobat_dc | 24.002.20991 and earlier; 24.002.20964 and earlier | Not stated |
| Adobe | acrobat | 24.001.30123 and earlier; 20.0 through 20.005.30636; 20.0 through 20.005.30635 | Not stated |
| Adobe | acrobat_reader_dc | 24.002.20964 and earlier; 24.002.20991 and earlier | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.0 | High | CNA (adobe.com) |
| CVSS 3.1 | 7.0 | High | NVD |
Official description
Acrobat Reader versions 20.005.30636, 24.002.21005, 24.001.30159, 20.005.30655, 24.002.20965, 24.002.20964, 24.001.30123, 24.003.20054 and earlier are affected by a Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability that could lead to arbitrary code execution. This vulnerability arises when the timing of actions changes the state of a resource between the checking of a condition and the use of the resource, allowing an attacker to manipulate the resource in a harmful way. Exploitation of this issue requires user interaction in that a victim must open a malicious file.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Time-of-check Time-of-use (TOCTOU) Race Condition
The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
How developers prevent this class of flaw
- The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
- When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
- Limit the interleaving of operations on files from multiple processes.
More Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities (CWE-367)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
Other vulnerabilities in Acrobat Reader
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
Recent Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities
- 7.0 High severity
- 7.5 High severity
- 7.5 High severity
- 7.8 High severity
- 7.0 High severity
- 7.0 High severity
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