CVE-2025-58058

It is possible to put data in front of an LZMA-encoded byte stream without detecting the situation while reading the header. This can lead to increased memory consumption because the current implementation allocates the full decoding buffer directly after reading the header. The LZMA header doesn't include a magic number or has a checksum to detect such an issue according to the specification.

Note that the code recognizes the issue later while reading the stream, but at this time the memory allocation has already been done.

Mitigations

The release v0.5.15 includes following mitigations:

• The ReaderConfig DictCap field is now interpreted as a limit for the dictionary size.
• The default is 2 Gigabytes - 1 byte (2^31-1 bytes).
• Users can check with the [Reader.Header] method what the actual values are in their LZMA files and set a smaller limit using ReaderConfig.
• The dictionary size will not exceed the larger of the file size and the minimum dictionary size. This is another measure to prevent huge memory allocations for the dictionary.
• The code supports stream sizes only up to a pebibyte (1024^5).

Note that the original v0.5.14 version had a compiler error for 32 bit platforms, which has been fixed by v0.5.15.

Methods affected

Only software that uses lzma.NewReader or lzma.ReaderConfig.NewReader is affected. There is no issue for software using the xz functionality.

I thank @GregoryBuligin for his report, which is provided below.

When unpacking a large number of LZMA archives, even in a single goroutine, if the first byte of the archive file is 0 (a zero byte added to the beginning), an error writeMatch: distance out of range occurs. Memory consumption spikes sharply, and the GC clearly cannot handle this situation.

Details

Judging by the error writeMatch: distance out of range, the problems occur in the code around this function.
https://github.com/ulikunitz/xz/blob/c8314b8f21e9c5e25b52da07544cac14db277e89/lzma/decoderdict.go#L81

PoC

Run a function similar to this one in 1 or several goroutines on a multitude of LZMA archives that have a 0 (a zero byte) added to the beginning.

const ProjectLocalPath = "some/path"
const TmpDir = "tmp"

func UnpackLZMA(lzmaFile string) error {
	file, err := os.Open(lzmaFile)
	if err != nil {
		return err
	}
	defer file.Close()

	reader, err := lzma.NewReader(bufio.NewReader(file))
	if err != nil {
		return err
	}

	tmpFile, err := os.CreateTemp(TmpDir, TmpLZMAPrefix)
	if err != nil {
		return err
	}
	defer func() {
		tmpFile.Close()
		_ = os.Remove(tmpFile.Name())
	}()

	sha256Hasher := sha256.New()
	multiWriter := io.MultiWriter(tmpFile, sha256Hasher)

	if _, err = io.Copy(multiWriter, reader); err != nil {
		return err
	}

	unpackHash := hex.EncodeToString(sha256Hasher.Sum(nil))
	unpackDir := filepath.Join(
		ProjectLocalPath, unpackHash[:2],
	)
	_ = os.MkdirAll(unpackDir, DirPerm)

	unpackPath := filepath.Join(unpackDir, unpackHash)

	return os.Rename(tmpFile.Name(), unpackPath)
}

Servers with a small amount of RAM that download and unpack a large number of unverified LZMA archives

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2025-58058 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.5.15); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-58058? CVE-2025-58058 is a medium-severity allocation of resources without limits or throttling vulnerability in github.com/ulikunitz/xz (go), affecting versions <= 0.5.13. It is fixed in 0.5.15. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2025-58058? CVE-2025-58058 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/ulikunitz/xz are affected by CVE-2025-58058? github.com/ulikunitz/xz (go) versions <= 0.5.13 is affected.
4. Is there a fix for CVE-2025-58058? Yes. CVE-2025-58058 is fixed in 0.5.15. Upgrade to this version or later.
5. Is CVE-2025-58058 exploitable, and should I be worried? Whether CVE-2025-58058 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-58058 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-58058? Upgrade github.com/ulikunitz/xz to 0.5.15 or later.